#include <iostream>

using namespace std;

int main()
{
    int N, res;
    cin >> N;
    
    res = 0;
    
    for(int i = 1; i <= N;i++){
        if(N == 1){
            res = 1;
        }else{
            res = res + i;
        }
    }
    
    cout << res;
    
    return 0;
}