#include<iostream.h>
#include<stdio.h>
int rezervor(int n)
{
	int r=0,i=0;
   do r+=i++; while(i<=n);
	return r;
};
void main()
{
   int m;
	cout<<"m=";cin>>m;
   cout<<rezervor(m)<<"\n";
   getchar();
}