#include <iostream>
#include <string>
#include <algorithm>
#include <numeric>

using namespace std;

int n;
string A, B;
long long max_nwd = 1;

// Szybka funkcja obliczająca NWD za pomocą algorytmu Euklidesa
long long gcd(long long a, long long b) {
    while (b) {
        a %= b;
        swap(a, b);
    }
    return a;
}

void dfs(int idx, long long cur_x, long long cur_y, long long max_possible_x, long long max_possible_y) {
    // Jeśli maksymalny możliwy wynik w tej gałęzi nie ma szans przebić obecnego max_nwd, odcinamy poddrzewo
    // Górne ograniczenie dla NWD(x, y) to min(x, y)
    if (min(max_possible_x, max_possible_y) <= max_nwd) {
        return;
    }

    if (idx == n) {
        if (cur_x > 0 && cur_y > 0) {
            long long current_nwd = gcd(cur_x, cur_y);
            if (current_nwd > max_nwd) {
                max_nwd = current_nwd;
            }
        }
        return;
    }

    int start_a = (A[idx] == '?') ? 0 : (A[idx] - '0');
    int end_a = (A[idx] == '?') ? 9 : (A[idx] - '0');

    int start_b = (B[idx] == '?') ? 0 : (B[idx] - '0');
    int end_b = (B[idx] == '?') ? 9 : (B[idx] - '0');

    for (int da = start_a; da <= end_a; ++da) {
        long long next_x = cur_x * 10 + da;
        long long next_max_x = max_possible_x * 10 + da;

        for (int db = start_b; db <= end_b; ++db) {
            long long next_y = cur_y * 10 + db;
            long long next_max_y = max_possible_y * 10 + db;

            dfs(idx + 1, next_x, next_y, next_max_x, next_max_y);
        }
    }
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    if (!(cin >> n >> A >> B)) return 0;

    // Obliczamy maksymalne możliwe wartości (gdzie '?' zamieniamy na '9')
    long long initial_max_x = 0, initial_max_y = 0;
    for (int i = 0; i < n; ++i) {
        int da = (A[i] == '?') ? 9 : (A[i] - '0');
        int db = (B[i] == '?') ? 9 : (B[i] - '0');
        initial_max_x = initial_max_x * 10 + da;
        initial_max_y = initial_max_y * 10 + db;
    }

    dfs(0, 0, 0, initial_max_x, initial_max_y);

    cout << max_nwd << "\n";

    return 0;
}