int strdiff(char *a, char *b){
    int index = 0;
    while(a[index] != '\0' && b[index] != '\0' && a[index] == b[index]){
        index++;
    }

    if(a[index] == '\0' && b[index] == '\0'){
        return -1;
    }
    char val = a[index]^b[index];
    int i = 0;
    while(val){
        if(val&1){
            return 8*index+i;
        }
        val = val >> 1;
        i++;
    }
}