# include<stdio.h> # include<iostream> //# include<cstring> using namespace std; int main(){ int n,sum=0,a[100],x=0; memset(a,0,sizeof(a)); while(cin>>n){ sum=0; for(int i=n;i>0;i--) sum+=i; a[x]=sum; x++; } for(int i=0;i<x;i++) cout<<a[i]<<endl; return 0; }