#include <bits/stdc++.h> using namespace std; using ll = long long; #define rep(i, n) for (int i = 0; i < (int)(n); i++) int main() { ll a,b,c=1,cnt=1; cin>>a>>b; if(b==0){ cout<<1<<endl; return 0; } for(int i=a; a<10; a++){ c *= i; cnt++; if(c==-1){ cout<<cnt<<endl; return 0; } } cout<<-1<<endl; }