#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

#define rep(i,n) for(i=0; i<n; ++i)
#define in(a) cin >> a
#define out(a,b) cout << a << b
using namespace std;

int main(void){
    int i, n, sum = 0;
    in(n);
    rep(i, n) sum += i+1;
    out(sum, endl);
    return 0;
}