#include<iostream> #include<string> #include<cstdio> #include<vector> #include<cmath> #include<algorithm> #include<functional> #include<iomanip> #include<queue> #include<ciso646> #include<random> #include<map> #include<set> #include<complex> #include<bitset> #include<stack> #include<unordered_map> using namespace std; typedef long long ll; typedef unsigned int ui; const ll mod = (ll)(1e+9) + 7; const ll INF = (ll)1000000007 * 1000000007; typedef pair<int, int> P; #define stop char nyaa;cin>>nyaa; #define rep(i,n) for(int i=0;i<n;i++) #define per(i,n) for(int i=n-1;i>=0;i--) #define Rep(i,sta,n) for(int i=sta;i<n;i++) #define rep1(i,n) for(int i=1;i<=n;i++) #define per1(i,n) for(int i=n;i>=1;i--) #define Rep1(i,sta,n) for(int i=sta;i<=n;i++) typedef long double ld; typedef complex<ld> Point; const ld eps = 1e-8; const ld pi = acos(-1.0); typedef pair<ll, ll> LP; typedef pair<ld, ld> LDP; typedef unsigned long long ul; ul gcd(ul a, ul b) { if (a < b)swap(a, b); while (b) { ul r = a % b; a = b; b = r; } return a; } int main() { ul n, m; cin >> n >> m; ul d = gcd(n, m); n /= d; m /= d; int c[2] = {}; while (m % 2 == 0) { m /= 2; c[0]++; } while (m % 5 == 0) { m /= 5; c[1]++; } while (n % 10 == 0)n /= 10; if (m > 1) { cout << -1 << endl; } else { if (c[0] > c[1]) { cout << 5 << endl; } else if (c[0] == c[1]) { cout << n % 10 << endl; } else { int nex = n % 10; rep(i, c[1] - c[0]) { nex = 2 * nex % 10; } cout << nex << endl; } } return 0; }