#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for (int i = x; i < n; i++)
#define OP(m) cout << m << endl
typedef long long ll;
typedef unsigned long long ull;

int main()
{
    string s;
    int a[10];
    while (cin >> s)
    {
        rep(i, 10)
        {
            a[i] = s[i] - '0';
        }
        int n = 9;
        rep(i, 10)
        {
            rep(i, n)
            {
                a[i] += a[i + 1];
            }
            n--;
        }
        OP(a[0] % 10);
    }
    return 0;
}
