input
723 9
ouput
157557417
code
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const double PI = acos(-1);
const int INF = 0x3f3f3f3f;
const int N = 3e5+10;
const int MOD = 1e9 + 7;
//
int n, m, f[N];
ll temp;
//
ll quick_pow(ll ans, ll p, ll res = 1) {
for(; p; p >>= 1, ans = ans * ans % MOD)
if(p & 1) res = res * ans % MOD;
return res % MOD;
}
ll inv(ll ans) {
return quick_pow(ans, MOD - 2) % MOD;
}
ll C(int n, int m) {
return 1ll * f[n] * inv(f[n - m]) % MOD * inv(f[m]) % MOD;
}
inline void solve(ll res = 0, ll ans = 0) {
res = C(2 * m + n - 1, 2 * m);
cout << res << endl;
}
int main() {
f[0] = f[1] = 1;
for(int i = 2; i < N; ++ i)
f[i] = 1ll * f[i - 1] * i % MOD;
cin >> n >> m;
solve();
return 0;
}