TONG1 C++

#include<bits/stdc++.h>
using namespace std;

int n;
long long s1,s2,s3;
int main()
{
    freopen("tong1.inp","r",stdin);
    freopen("tong1.out","w",stdout);
    cin>>n;
    //Tinh S1
    s1=0;
    for(int i=1;i<=n;i++) 
        s1=s1+i;
    cout<<"S1 = "<<S1<<endl;
    //Tinh S2
    s2=1;
    for(int i=1;i<=n;i++) 
        s2=s2*i;
    cout<<"S2 = "<<s2<<endl;
    //Tinh S3
    s3=0;
    for(int i=1;i<=n;i++) 
        s3=s3+i*i;
    cout<<"S3 = "<<s3;
}