#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[])
{
    int res = 0;
    char buf[5];
    char *end;
    for (int i = 0; i < strlen(argv[1]); i+=4) {
        buf[0] = argv[1][i];
        buf[1] = argv[1][i+1];
        buf[2] = argv[1][i+2];
        buf[3] = argv[1][i+3];
        buf[4] = '\0';
        res ^= strtol(buf, &end, 16);
    }
    printf("Checksum 0x%x\n", res);
    return 0;
}