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

typedef long long ll;
typedef unsigned long long ull;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define pb push_back

int f(int n) {
    if(n == 0) return 1;
    else
        return f(n-1) + n;
}

int main() {
    int n;
    while(cin >> n) {
        cout << f(n) << endl;
    }
    
    return 0;
}