#include <iostream>
using namespace std;

int main(){
    int n , sum =0;
    cout<<"enter the value of n:"<<endl;
    cin>>n;

    for(int i = 1; i<=n; i++){
        sum+= i;
    }
    
    cout<<"sum of natural numbers."<<endl;
    cout<<sum<<endl;
    
    return 0;
}