简单的一个数学定理
#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long LL;
const int N = 1010;

int n,m;
LL res;

int main(){
    scanf("%d%d",&n,&m);
    res = (LL)n * m - n - m;
    printf("%lld\n",res);
    return 0;
}