用二分法！用long long！！

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll jz(ll &rad, string &s){
    ll t = 0;
    for(ll i = 0; i < s.size(); ++i){
        if(isdigit(s[i]))
            t = t * rad + s[i] - '0';
        else
            t = t * rad + s[i] - 'a' + 10;
    }
    return t;
}
ll find_(string &s){
    ll t = 0;
    ll r;
    for(ll i = 0; i < s.size(); ++i){
        if(isdigit(s[i]))
            r = s[i] - '0';
        else
            r = s[i] - 'a' + 10;
        if(t < r) t = r;
    }
    return t+1;
}
int main(){
     string s[3];
     ll pos,radix;
     ll a[3] = {0};
     cin >> s[1] >> s[2] >> pos >> radix;
     a[pos] = jz(radix,s[pos]);
     ll mr = find_(s[3-pos]);
     radix = 10;
     ll l = mr, r = a[pos] + 1,mid;
      //if(l > r) swap(l,r);
     while(l <= r){
        mid = (l + r) / 2;
        ll temp = jz(mid,s[3-pos]);
         if(temp == a[pos]){
            cout << mid; return 0;
         }
         else if(temp > a[pos] || temp < 0) r = mid - 1;
         else l = mid + 1;
     }
    cout << "Impossible";
    return 0;


}