题解在此

#include <iostream>
using namespace std;
int main(){
    int n;
    cin>>n;
    int ans=0;
    for (int i=1;i<=n;i++){
        int sum=1;
        for (int j=1;j<=i;j++){
            sum*=j;
        }
        ans+=sum;
    }
    cout<<ans;
    return 0;
}