#include "bits/stdc++.h"
#pragma GCC optimize("Ofast")

// Begin {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

template <class A, class B> inline bool chmax(A &a, const B &b) { return b > a && (a = b, true); }
template <class A, class B> inline bool chmin(A &a, const B &b) { return b < a && (a = b, true); }

template <class T>
inline vector<T> make_v(const T &initvalue, size_t sz) {
    return vector<T>(sz, initvalue);
}

template <class T, class... Args>
inline auto make_v(const T &initvalue, size_t sz, Args... args) {
    return vector<decltype(make_v<T>(initvalue, args...))>(sz, make_v<T>(initvalue, args...));
}

constexpr int INF = 0x3f3f3f3f;
constexpr int64_t LINF = 0x3f3f3f3f3f3f3f3fLL;
// }}} End

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    size_t N; cin >> N;

    unsigned long long mul = 1;
    for (size_t i = 0; i < N; ++i) {
        unsigned long long p; cin >> p;
        mul *= p;
    }

    while (true) {
        if (to_string(mul).length() == 1) {
            return cout << mul << "\n", 0;
        } else {
            unsigned long long sum = 0;
            while (mul > 0) {
                sum += mul % 10;
                mul /= 10;
            }
            mul = sum;
        }
    }

    return 0;
}