C++ :

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,sum=0,y=1;
    cin>>n;
    while(n--){
        sum+=y;
        if(n==0) break;
        y++; 
    }
    cout<<sum;
    return 0;
} 

Python :

# coding=utf-8
n=int(input())
s=0
for i in range(n+1):
    s=s+i
print(s)