#include <bits/stdc++.h>

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

    int N;

    std::cin >> N;

    if (N >= 10) {
        std::cout << 10;
        return 0;
    }

    std::set<int> inside;

    int mex = 1;

    for (int i = 1; i <= N; i++) {
        int val = i;
        int rev = 0;

        while (val > 0) {
            rev = rev * 10 + val % 10;
            val /= 10;
        }

        inside.insert(rev);
    }

    while (inside.find(mex) != inside.end()) mex++;

    std::cerr << mex;

    return 0;
}