#include<bits/stdc++.h>
using namespace std;
int main(){
    int s=0,n,i=1;
    cin>>n;
    while(i<=n){
        s=s+i;
        i++;
    }
    cout<<s;
    return 0;
}
/**************************************************************
	Problem: 1002
	User: binzicheng1
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/