A 求导

题目地址：

https://ac.nowcoder.com/acm/contest/5389/A

基本思路：

参考代码：

#pragma GCC optimize(2)
#pragma GCC optimize(3)
#include <bits/stdc++.h>
using namespace std;
#define IO std::ios::sync_with_stdio(false)
#define int long long
#define rep(i, l, r) for (int i = l; i <= r; i++)
#define per(i, l, r) for (int i = l; i >= r; i--)
#define mset(s, _) memset(s, _, sizeof(s))
#define pb push_back
#define pii pair <int, int>
#define mp(a, b) make_pair(a, b)
#define INF 0x3f3f3f3f

const int mod = 1e9 + 7;
int n;
signed main() {
  IO;
  cin >> n;
  int res = 1;
  rep(i,1,n){
    res = res * i % mod;
  }
  cout << res << '\n';
  return 0;
}