1010

#include <iostream>

#include <cctype>

#include <algorithm>

#include <cmath>

using namespace std;

long long convert(string n, long long radix) {

    long long sum = 0;

    int index = 0, temp = 0;

    for (auto it = n.rbegin(); it != n.rend(); it++) {

        temp = isdigit(*it) ? *it - '0' : *it - 'a' + 10;// - 'a' + 10 transform letter to 10radix number;-'0' transform string to number;(a-z represent the decimal numbers 10-35.)

        sum += temp * pow(radix, index++);

    }

    return sum;

}

long long find_radix(string n, long long num) {

    char it = *max_element(n.begin(), n.end());

    long long low = (isdigit(it) ? it - '0' : it - 'a' + 10) + 1;

    long long high = max(num, low);

    while (low <= high) {

        long long mid = (low + high) / 2;

        long long t = convert(n, mid);

        if (t < 0 || t > num) //if t is negative number,that mean t out of long long boundary.

            high = mid - 1;

        else if (t == num) return mid;

        else low = mid + 1;

    }

    return -1;

}

int main() {

    string n1, n2;

    long long tag = 0, radix = 0, result_radix;

    cin >> n1 >> n2 >> tag >> radix;

    result_radix = tag == 1 ? find_radix(n2, convert(n1, radix)) : find_radix(n1, convert(n2, radix));

    if (result_radix != -1) {

        printf("%lld", result_radix);

    }

    else {

        printf("Impossible");

    }

    return 0;

}