#include <stdio.h>

double f2c(double f);
double input_double(void);

int main(void) {
    printf("Enter Fahrenheit temperature: ");

    double f;
    f = input_double();

    printf("Celsius is %f\n", f2c(f));
    printf("For reference: \n");
    printf("Boiling is %f and freezing is %f\n",
            f2c(212), f2c(32));
    return 0;
}

double f2c(double f) {
    return (f-32) * 5/9;
}

double input_double(void) {
    double x;
    scanf("%lf", &x);
    return x;
}