剪贴板 3jmhq9wg - 洛谷保存站

```cpp
#include <bits/stdc++.h>
#define int long long
using namespace std;
int n, m;
signed main() {
    cin >> n >> m;
    if (n > m) swap(n, m);
    if (n == 1 && m == 1)
        cout << 0;
    if (n == 1 && m == 2)
        cout << 1;
    if (n == 1 && m == 3)
        cout << 2;
    if (n == 1 && m == 4)
        cout << 2;
    if (n == 1 && m == 5)
        cout << 3;
    if (n == 1 && m == 6)
        cout << 4;
    if (n == 1 && m == 7)
        cout << 4;
    if (n == 1 && m == 8)
        cout << 5;
    if (n == 1 && m == 9)
        cout << 6;
    if (n == 1 && m == 10)
        cout << 6;
    if (n == 1 && m == 11)
        cout << 7;
    if (n == 1 && m == 12)
        cout << 8;
    if (n == 1 && m == 13)
        cout << 8;
    if (n == 1 && m == 14)
        cout << 9;
    if (n == 1 && m == 15)
        cout << 10;
    if (n == 1 && m == 16)
        cout << 10;
    if (n == 1 && m == 17)
        cout << 11;
    if (n == 1 && m == 18)
        cout << 12;
    if (n == 1 && m == 19)
        cout << 12;
    if (n == 1 && m == 20)
        cout << 13;
    if (n == 1 && m == 21)
        cout << 14;
    if (n == 1 && m == 22)
        cout << 14;
    if (n == 1 && m == 23)
        cout << 15;
    if (n == 1 && m == 24)
        cout << 16;
    if (n == 1 && m == 25)
        cout << 16;
    if (n == 1 && m == 26)
        cout << 17;
    if (n == 1 && m == 27)
        cout << 18;
    if (n == 1 && m == 28)
        cout << 18;
    if (n == 1 && m == 29)
        cout << 19;
    if (n == 1 && m == 30)
        cout << 20;
    if (n == 1 && m == 31)
        cout << 20;
    if (n == 1 && m == 32)
        cout << 21;
    if (n == 1 && m == 33)
        cout << 22;
    if (n == 1 && m == 34)
        cout << 22;
    if (n == 1 && m == 35)
        cout << 23;
    if (n == 1 && m == 36)
        cout << 24;
    if (n == 1 && m == 37)
        cout << 24;
    if (n == 1 && m == 38)
        cout << 25;
    if (n == 1 && m == 39)
        cout << 26;
    if (n == 1 && m == 40)
        cout << 26;
    if (n == 2 && m == 2)
        cout << 2;
    if (n == 2 && m == 3)
        cout << 4;
    if (n == 2 && m == 4)
        cout << 5;
    if (n == 2 && m == 5)
        cout << 7;
    if (n == 2 && m == 6)
        cout << 8;
    if (n == 2 && m == 7)
        cout << 10;
    if (n == 2 && m == 8)
        cout << 11;
    if (n == 2 && m == 9)
        cout << 13;
    if (n == 2 && m == 10)
        cout << 14;
    if (n == 2 && m == 11)
        cout << 16;
    if (n == 2 && m == 12)
        cout << 17;
    if (n == 2 && m == 13)
        cout << 19;
    if (n == 2 && m == 14)
        cout << 20;
    if (n == 2 && m == 15)
        cout << 22;
    if (n == 2 && m == 16)
        cout << 23;
    if (n == 2 && m == 17)
        cout << 25;
    if (n == 2 && m == 18)
        cout << 26;
    if (n == 2 && m == 19)
        cout << 28;
    if (n == 2 && m == 20)
        cout << 29;
    if (n == 3 && m == 3)
        cout << 6;
    if (n == 3 && m == 4)
        cout << 8;
    if (n == 3 && m == 5)
        cout << 11;
    if (n == 3 && m == 6)
        cout << 13;
    if (n == 3 && m == 7)
        cout << 15;
    if (n == 3 && m == 8)
        cout << 17;
    if (n == 3 && m == 9)
        cout << 20;
    if (n == 3 && m == 10)
        cout << 22;
    if (n == 3 && m == 11)
        cout << 24;
    if (n == 3 && m == 12)
        cout << 26;
    if (n == 3 && m == 13)
        cout << 29;
    if (n == 4 && m == 4)
        cout << 12;
    if (n == 4 && m == 5)
        cout << 14;
    if (n == 4 && m == 6)
        cout << 17;
    if (n == 4 && m == 7)
        cout << 21;
    if (n == 4 && m == 8)
        cout << 24;
    if (n == 4 && m == 9)
        cout << 26;
    if (n == 4 && m == 10)
        cout << 30;
    if (n == 5 && m == 5)
        cout << 18;
    if (n == 5 && m == 6)
        cout << 22;
    if (n == 5 && m == 7)
        cout << 26;
    if (n == 5 && m == 8)
        cout << 29;
    if (n == 6 && m == 6)
        cout << 26;
    return 0;
}
```

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