#include <iostream>
#include <algorithm>
#include <unordered_set>
using namespace std;
int main()
{
    long long n, m;
    while (cin>>n>>m) {
        unordered_set<long long> s;
        auto res=-1LL;
        while (true) {
            auto t=n%m;
            if (!t) {
                n/=m;
                while (n%10==0) n/=10;
                res=n%10;
                break;
            }
            if (s.count(t)) { res=-1; break; }
            s.insert(t);
            n%=m;
            n*=10;
        }
        cout<<res<<endl;
    }
}