#include <cs50.h>
#include <stdio.h>

int sigma(int m);

int main(void)
{
    int n;
    do
    {
        printf("Positive integer please: ");
        n = get_int();
    }
    while (n < 1);

    int answer = sigma(n);

    printf("%i\n", answer);
}

int sigma(int m)
{
    if (m <= 0)
    {
        return 0;
    }
    else
    {
        return (m + sigma(m - 1));
    }
}