#include <stdio.h>
#include <assert.h>
#include <math.h>

double sqrt2(double x)
{
    assert(x>=0.0);
    return sqrt(x);
}

int main()
{
    printf("Golden ratio: %lg\n", (1.0 + sqrt2(5))/2.0);
    printf("Bad ratio: %lg\n", (1.0 + sqrt2(-5))/2.0);
}