#include <stdio.h>

int main()
{
    int n, sum, d;

    printf("Enter a number to check if it's happy: ");
    scanf("%d", &n);

    while (n > 0) {
        sum = 0;
        while (n > 0) {
            d = (n%10);
            n/=10;
            sum += d*d;
        }
        n = sum;

        if ( n < 10 )
            break;
    }

    if (n == 1)
        printf("Happy number!");
    else
        printf("Not a happy number.");

    return 0;
}