2016春季练习——水题

来源：HDU 1002

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;

int main(){
    long long n;
    while(scanf("%lld",&n)!=EOF){
        cout<<n*(n+1)/2<<endl<<endl;
    }
    return 0;
}