AC程式碼：

#include <iostream>
#include <stdio.h>
#include <algorithm>

using namespace std;

typedef long long LL;
const LL mod = 1000000007;
const int maxn = 100010;
LL JC[maxn];
void createTable() {
    JC[0] = 1;
    for(int i = 1; i < maxn; i++) {
        JC[i] = (i*JC[i-1])%mod;
    }
}
LL resMod(LL x,LL pow) {
    LL ans,res;
    ans = 1;
    res = x;
    while(pow) {
        if(pow&1) {
            ans = (ans*res)%mod;
        }
        res = (res*res)%mod;
        pow = pow>>1;
    }
    return ans;
}
LL C(int n,int m) {
    LL temp = (JC[m]*JC[n-m])%mod;
    //求temp的逆元，由於mod是素數，因此可以用小費馬定理求逆元
    LL resTemp = resMod(temp,mod-2);
    LL ans = (JC[n]*resTemp)%mod;
    return ans;
}
int main() {
    int N,M;
    createTable();
    while(~scanf("%d%d",&N,&M)) {
        int Min = min(N,M);
        int Max = max(N,M);
        LL ans = 0;
        for(int i = 0; i <= Min-2; i++) {
            ans += C(Min-2,i)*C(Max-2,i);
            ans = ans%mod;
        }
        printf("%lld\n",ans);
    }
    return 0;
}