#include #define EPS 1e-9 #define INF 1070000000LL #define MOD 1000000007LL #define fir first #define foreach(it,X) for(auto it=(X).begin();it!=(X).end();it++) #define numa(x,a) for(auto x: a) #define ite iterator #define mp make_pair #define mt make_tuple #define rep(i,n) rep2(i,0,n) #define rep2(i,m,n) for(int i=m;i<(n);i++) #define pb push_back #define pf push_front #define sec second #define sz(x) ((int)(x).size()) #define ALL( c ) (c).begin(), (c).end() #define gcd(a,b) __gcd(a,b) #define mem(x,n) memset(x,n,sizeof(x)) #define endl "\n" using namespace std; template void deploy(std::ostream &os, const TUPLE &tuple){} template void deploy(std::ostream &os, const TUPLE &t){ os << (POS == 0 ? "" : ", ") << get(t); deploy(os, t); } template std::ostream& operator<<(std::ostream &os, std::vector &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; } template std::ostream& operator<<(std::ostream &os, std::set &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; } template std::ostream& operator<<(std::ostream &os, std::map &mp){ int remain = mp.size(); os << "{"; for(auto e: mp) os << "(" << e.first << " -> " << e.second << ")" << (--remain == 0 ? "}" : ", "); return os; } #define DEBUG1(var0) { std::cerr << (#var0) << "=" << (var0) << endl; } #define DEBUG2(var0, var1) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG1(var1); } #define DEBUG3(var0, var1, var2) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG2(var1,var2); } #define DEBUG4(var0, var1, var2, var3) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG3(var1,var2,var3); } using ll = long long; int main(){ cin.tie(0); ios_base::sync_with_stdio(0); ll N,M; cin >> N >> M; ll a = gcd(N,M);N /= a;M/= a; if(M == 1){ while(N!= 0 && N % 10 == 0){ N /= 10; } cout << N << endl; }else{ while(M != 0 && M % 10 == 0){ M /= 10; } if(M == 1){ while(N!= 0 && N % 10 == 0){ N /= 10; } cout << N << endl; }else{ if(M % 2 != 0 && M % 5 != 0){ cout << -1 << endl; }else{ int div; if(M % 2 == 0){ div = 2; }else{ div = 5; } ll tmpM = M; int divc = 0; while(tmpM!= 0 && tmpM%div == 0){ tmpM /= div; divc += 1; } if(tmpM != 1){ cout << -1 << endl; }else{ N %= 10; rep(i,divc){ N*= (7-div); N %= 10; } cout << N << endl; } } } } return 0; }