题解

#include<bits/stdc++.h>
using namespace std;
int n,m1;
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
        int m=1,i1=i;
        while(i1){m*=i1;i1--;}
        m1+=m;
    }
    cout<<m1;
    return 0;
}