#include<bits/stdc++.h>
#define in cin
#define out cout
using namespace std;
typedef long long ll;
ll cmmdc(ll a,ll b){if(!b) return a;return cmmdc(b,a%b);}
int main(){
    #ifndef ONLINE_JUDGE
    ifstream in("test.in");
    ofstream out("test.out");
    #endif
    ll a,b;in>>a>>b;
    for(ll l=b-a+1;;l--) for(ll x=a;x+l-1<=b;x++) if(cmmdc(x,x+l-1)==1){out<<l<<'\n';return 0;}
    return 0;
}