#include<iostream>
#include<string>
#include<vector>
#include<cstdio>
#include<cstdlib>
#define N 10
using namespace std;

int main(){
    string inp;
    while(cin >>inp){
        vector<int> vec;
        for(int i = 0; i < N; i++){
            if(inp[i] == '0'){
                vec.push_back(0);
            } else{
                vec.push_back((int)inp[i] - '0');
            }
        }
        while(vec.size() > 1){
            vector<int> tmpvec;
            for(int i = 0; i < vec.size() - 1; i++){
                tmpvec.push_back((vec[i] + vec[i + 1]) % 10);
            }
            vec = tmpvec;
        }
        cout <<vec[0] <<endl;
    }
    return 0;
}