#include<bits/stdc++.h>
#define in cin
#define out cout
#define abs(x) ((x>0)?(x):(-(x)))
#define max(a,b) ((a)>(b)?(a):(b))
#define min(a,b) ((a)<(b)?(a):(b))
#define FOR(i, a, b) for(int i = a; i <= b; ++i)
#define DOWNFOR(i, a, b) for(int i = a; i >= b; --i)
#define FOREACH(i, t) for (typeof(t.begin()) i = t.begin(); i != t.end(); ++i)
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;
    ll ans=0;
    for(ll x=a;x<=a+10000;x++){
        for(ll y=b;y>=max( x+ans-2 , max(x+1,b-10000) );y--){
            if( cmmdc(x,y)==1 ) ans=max(ans,y-x+1);
        }
    }
    out<<ans<<'\n';
    return 0;
}