#include <stdio.h>

double max(double x, double y);

int main(void) {
    double a, b, c, d;

    a = 3.2;
    b = 7.5;
    c = 2.1;
    d = 5.8;

    printf("最大値は %.1f です\n", max(max(a, b), max(c, d)));

    return 0;
}

double max(double x, double y) {
    return (x > y) ? x : y;
}