#include <iostream>
#include <string>
using namespace std;

int main(void){
  int w[10];
  string str;

  while(cin >> str){
    int num = 10;
    for(int i = 0 ; i < num ; i++) w[i] = str[i] - '0';

    int a[10] = {0};
    while(num > 1){
      for(int i = 1 ; i < num ; i++){
        a[i-1] = (w[i-1] + w[i]) % 10;
      }  
      for(int i = 0 ; i < num ; i++) w[i] = a[i];
      num--;
    }
    
    cout << a[0] << endl;
  }

  return 0;
}