#include <stdio.h>

int main()
{
    int i;
    extern int formula1(int n), formula2(int n);

    for (i = 1; i <= 100; i++)
	if (formula1(i) != formula2(i))
	    printf("formula doesn't work for n=%d\n", i);
    
    return 0;
}


int formula1(int n)
{
    int i, sum;
    sum = 0;
    for (i = 1; i <= n; i++)
	sum = sum + i;
    return sum;
}


int formula2(int n)
{
    return (n * n + n) / 2;
}