#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

int charToInt(char c) {
    if (c >= '0' && c <= '9') return c - '0';
    if (c >= 'A' && c <= 'Z') return c - 'A' + 10;
    if (c >= 'a' && c <= 'z') return c - 'a' + 10;
    return 0;
}

char intToChar(int x) {
    if (x < 10) return '0' + x;
    return 'A' + (x - 10);
}

string add(const string& a, int jz) {
    string b(a);
    reverse(b.begin(), b.end());
    string tmp(a.size() + 1, '0');
    int carry = 0;
    for (size_t i = 0; i < a.size(); i++) {
        int ia = charToInt(a[i]);
        int ib = charToInt(b[i]);
        int sum = ia + ib + carry;
        carry = sum / jz;
        tmp[i] = intToChar(sum % jz);
    }
    if (carry > 0) tmp[a.size()] = intToChar(carry);
    else tmp.pop_back();
    return tmp;
}

bool check(const string& x) {
    return equal(x.begin(), x.begin() + x.size()/2, x.rbegin());
}

int main(){
    int jz;
    string n;
    cin >> jz >> n;
    for (int i = 0; i <= 30; i++) {
        if (check(n)) {
            cout << "STEP=" << i << endl;
            return 0;
        }
        n = add(n, jz);
    }
    cout << "Impossible!" << endl;
}