#include <stdio.h>

int add(int a); //function declaration

int main (void)
{
    int b,sum;

    printf("\nEnter a number: ");
    scanf("%d", &b);

    sum = add(b); //function calling

    printf("\nSum: %d\n\n", sum);

    return 1;
}

int add(int a) //function definition    
{
    int result = 0;
    for(int i = 0; i < a; i++)
    {
        result = result + i;
    }

    return result;
}