2659: [Beijing wc2012]算不出的算式

2659: [Beijing wc2012]算不出的算式

题目戳这 

题解戳这

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;

int main() {
    LL a,b;cin >> a >> b;
    if (a == b) cout << (a * b - 1) / 4;
    else cout << (a - 1) * (b - 1) / 4;
    return 0;
}