binary_to_hex

#include <stdio.h>

void bintohex() {
    char k, l, m, n;
    int x;
    scanf("%c", &k);
    scanf("%c", &l);
    scanf("%c", &m);
    scanf("%c", &n);
    k = k - '0';
    l = l - '0';
    m = m -'0';
    n = n - '0';
    x = k*8 + l*4 + m*2 + n;
    if (feof(stdin)) return;

    printf("%X", x);

}

int main () {

    for (; !feof(stdin);)
        bintohex();

    return 0;
}