---

#include <iostream>
#include <string>
#include <cmath>
using namespace std;
int main() {
    int n;
    if (!(cin >> n)) {
        cout << "Error! Invalid vector." << endl;
        return 0;
    }

    string vector;
    cin >> vector;

    size_t required_length = 1ULL << n;

    if (vector.length() != required_length) {
        cout << "Error! Invalid vector." << endl;
        return 0;
    }

    unsigned long long index = 0;

    for (char c : vector) {
        if (c != '0' && c != '1') {
            std::cout << "Error! Invalid vector.\n";
            return 0;
        }

        index = (index << 1) + (c - '0');
    }

    std::cout << index << "\n";

    return 0;
}