#include <iostream> #include <vector> using namespace std; long long gdc(long long A, long long B) { long long c=A%B; while(c) { A=B; B=c; c=A%B; } return B; } int main() { int64_t a,b; cin>>a>>b; bool ok=1; while(a<b && ok) { for(int64_t i=a;i<b && ok;i++) if(gdc(i,b)==1LL) { ok=0; cout<<b-i+1; return 0; } b--; } if(ok) cout<<-1; }