//
//  main.cpp
//  lecture6_hw2
//
//  Created by Михаил Мустакимов on 16.11.17.
//  Copyright © 2017 Mikhail Mustakimov. All rights reserved.
//

#include <iostream>
#include <string>

using namespace std;

short calcCheckNum(short n, short ln) {
    short tmp = n * ((ln % 2 == 0)? 1 : 2);
    tmp = (tmp > 9)? (tmp-9)%10 : tmp;
    return tmp;
}

int main(int argc, const char * argv[]) {
    string number;
    getline(cin, number);
    long sum = 0;
    long ln = 0;
    long xcount = 0;
    short xln = 0;
    for (long i=number.length()-1; i>=0; i--) {
        char ch = number[i];
        if (ch >= '0' && ch <= '9') {
            short n = ch - '0';
            sum += calcCheckNum(n, ln++);
        }
        if (ch == 'X' || ch == 'x'){
            xcount++;
            xln = ln++;
        }
    }
    if (xcount != 1){
        cout << "WRONG";
        return 0;
    }
    for (int i=0; i<10; i++) {
        long tmp = sum + calcCheckNum(i, xln);
        if (tmp % 10 == 0) {
            cout << i << endl;
            break;
        }
    }
    return 0;
}