#include using namespace std; #define FOR(i,a,b) for(int i=(a);i<(b);i++) #define REP(i,n) FOR(i,0,n) #define ALL(v) (v).begin(),(v).end() #define fi first #define se second template inline bool chmax(A &a, B b) { if (a inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; } typedef unsigned long long ull; typedef long long ll; typedef pair pii; typedef pair pll; typedef pair P; const ll INF = 1ll<<29; const ll MOD = 1000000007; const double EPS = 1e-10; ll gcd(ll a, ll b) { if (b == 0) return a; return gcd(b, a % b); } int main() { ll n, m; cin >> n >> m; ll g = gcd(n, m); n /= g; m /= g; if (n % m == 0) { stringstream ss; ss << n / m; string str = ss.str(); int ans; REP(i, str.size()) if (str[i] != '0') ans = str[i] - '0'; cout << ans << endl; return 0; } int cnt2 = 0, cnt5 = 0; while (m % 2 == 0) cnt2++, m /= 2; while (m % 5 == 0) cnt5++, m /= 5; if (m != 1) puts("-1"); else { while (n % 10 == 0) n /= 10; n %= 10; REP(i, cnt5) n = n * 2 % 10; REP(i, cnt2) n = n * 5 % 10; cout << n << endl; } return 0; }