#include <bits/stdc++.h> #define int64 long long #define pb push_back #define mp make_pair #define INF numeric_limits<int>::max() using namespace std; int64 gcd(int64 a,int64 b) { int64 r; r=a%b; while(r) { a=b; b=r; r=a%b; } return b; } int64 x,y; int main() { cin>>x>>y; if(x==1 && y==1) { cout<<"1\n"; return 0; } int64 mx=-1; for(int64 i=y;i>x;i--) { for(int64 j=x;j<i;j++) if(gcd(i,j)==1) { mx=max(mx,i-j+1); break; } if(mx>=i-x)break; } cout<<mx<<'\n'; return 0; }