#include <iostream>
#include <algorithm>
#include <string>
using namespace std;
typedef long long LL;

int get(char c)
{
    if(c <= '9') return c - '0';
    return c - 'a' + 10; 
}
LL cal(string n,LL radix)
{
    LL ret = 0;
    for(auto c : n)
    {
        //无解
        if((double)ret * radix + get(c) > 1e16) return 1e16;
        ret = ret * radix + get(c);
    }
    return ret;
}
int main()
{
    string n1,n2;
    cin >> n1 >> n2;
    int tag,radix;
    cin >> tag >> radix;
    if(tag == 2) swap(n1,n2);
    LL target = cal(n1,radix);
    LL l = 0,r = target + 1;
    for(auto c : n2) l = max(l,(LL) get(c) + 1);
    while(l < r)
    {
        LL mid = (l + r) >> 1;
        if(cal(n2,mid) >= target) r = mid;
        else l = mid + 1;
    }
    if(cal(n2,l) != target) cout << "Impossible";
    else cout << l;
    return 0;
}