C :

#include<stdio.h>
int main()
{
	int n,i,sum=0;
	scanf("%d",&n);
	for(i=1;i<=n;i++)
	{
	  sum+=i;
	}
  printf("%d\n",sum);
  return 0;
}

C++ :

#include<iostream>
using namespace std;
int main()
{
	int a;
	while(cin>>a)
	cout<<a*(a+1)/2<<endl;
	return 0;
}