#include <iostream>
#include <string>
#include <unordered_map>
#include <algorithm>

bool base_check(const std::string& str, int base) {
    if (base < 2 || base > 36) return false;

    static const std::unordered_map<int, std::string> baseDigits = []{
        std::unordered_map<int, std::string> m;
        for (int b = 2; b <= 36; ++b) {
            std::string digits;
            for (int i = 0; i < b; ++i)
                digits += (i < 10) ? ('0' + i) : ('a' + i - 10);
            m[b] = digits;
        }
        return m;
    }();

    const std::string& digits = baseDigits.at(base);
    for (char c : str) {
        char lc = std::tolower(static_cast<unsigned char>(c));
        if (digits.find(lc) == std::string::npos) return false;
    }
    return true;
}

int main() {
    std::cout << (base_check("10101", 2) ? "valid" : "invalid") << '\n';
    return 0;
}