# include <iostream>
# include <algorithm>
# define endl '\n'

using namespace std;

unsigned long long m, n, x, k, k2;

int cmmdc ( int a, int b )
{
    int c;
    while ( b )
    {
        c = a % b;
        a = b;
        b = c;
    }

    return a;
}

int main ()
{
    cin >> n >> m;
    unsigned long long maxim = 0;
    while ( m > maxim )
    {
        x = n;
        while ( cmmdc ( x, m ) != 1 && x < m )
            x ++;
        if ( cmmdc ( x, m ) == 1 )
            maxim = max ( maxim, m - x + 1 );

        m --;

    }

    cout << maxim;



    return 0;
}