#include "bits/stdc++.h"
#define int long long
#define range(i, a, b) for(auto i = a; i < b; i++)
#define rep(i, a) range(i, 0, a)
#define all(a) (a).begin(),(a).end()
using namespace std;
const int INF = sizeof(int) == sizeof(long long) ? 1000000000000000000LL : 1000000000;
const int MOD = 1000000007;
const long double EPS = 1e-8;
using vi = vector <int>;
using vvi = vector <vi>;

signed main() {
	string s;
	while(cin >> s) {
		while (s.size() != 1) {
			string tmp = "";
			rep (j, s.size() - 1){
				tmp += '0' + ((s[j] - '0') + (s[j + 1] - '0')) % 10;
			}
			s = tmp;
		}
		cout << s << endl;
	}
}
