#include #define REP(i, x, n) for(int i = x; i < (int)(n); i++) #define rep(i, n) REP(i, 0, n) #define all(x) (x).begin(), (x).end() #define rall(x) (x).rbegin(), (x).rend() #define F first #define S second #define mp make_pair using namespace std; typedef long long ll; typedef unsigned long long ull; typedef pair P; int main() { // ios_base::sync_with_stdio(false); ull N, M; cin >> N >> M; if(N % M == 0) { ull ans = N / M; while(ans % 10 == 0) ans /= 10; cout << ans % 10 << endl; } else { set> d; N %= M; int ans = 0; while(N % M) { while(N < M) N *= 10; int v = N / M; if(d.count(mp(N, v))) { ans = -1; break; } d.insert(mp(N, v)); ans = v; N %= M; } cout << ans << endl; } return 0; }