#include<stdio.h>
#include<stdlib.h>

int sum(int a)
{
    int i,ret;
    ret=0;
    for(i=1;i<=a;i++)
    	ret=ret+i;
    
    return ret;
}


int main()
{
    int n;
    printf("Enter number: ");
    scanf("%d",&n);
    
    printf("%d\n",sum(n));
    
    system("pause");
}