ub-if-goldbach-was-wrong.c

#include <stdio.h>

int bar(unsigned int x) {
    for (int i = x - 1; i >= 2; i--)
        for (int s = x; s >= 0; s -= i)
            if (s == 0)
                return 0;
    return 1;
}

int foo(unsigned int x) {
    if (x <= 2 || (x & 1) != 0)
        return 1;
    for (int i = x; i > 0; i--)
        if (bar(i) && bar(x - i))
            return i + 1;
    return 0;
}

int main() {
    int a;
    
    int x;
    scanf("%X", &x);
    if (foo(x) != 0)
        a = 0;

    return a;
}