hexen

#include <stdio.h>
#include "string.h"
#include "malloc.h"

int main() {
    char x[1000000];
    scanf("%s", &x);
    int len = strlen(x), sz = len * 4 + 1;
    char* ans = (char*) malloc(sz);
    memset(ans, '0', sz);
    ans[sz - 1] = 0;
    for (int i = 0; i < len; i++) {
        int tmp = 0;
        if (x[i] >= '0' && x[i] <= '9')
            tmp = x[i]-'0';
        else
            tmp = 10 + (x[i] - 'A');
        int k = 3;

        while (tmp > 0) {
            int t = tmp & 1;
            ans[i * 4 + k] = '0' + t;
            tmp >>= 1;
            k--;
        }
    }
    int len2 = len*4, chek = 0, diff = 0;
    for (int i = 0; i < len2; i++) {
        if (ans[i] != '0') {
            chek = 1;
            diff = i;
            break;
        }
    }
    printf("%s", chek ? ans + diff : "0");
    free(ans);
    return 0;
}