#include <stdio.h>

void hello(void) {
    puts("Hello, World!");
}

void byebye(void) {
    puts("Good bye, World!");
}

int main(void) {
    void (*work)(void) = hello;
    for (int i = 0; i < 10; i++) work();
    work = byebye;
    for (int i = 0; i < 10; i++) work();
    return 0;
}