#include <iostream>

using namespace std;

long long a , b;

long long cmmmdc ( long long x , long long y )
{
    long long r;
    while ( y != 0 )
    {
        r = x % y;
        x = y;
        y = r;
    }
    return x;
}

int main()
{
    cin >> a >> b;
    if ( cmmmdc(a,b) == 1 )
        cout << b-a+1 ;
    else
    {
        long long alfa = a;
        long long poz = a+1;
        long long amax = 0;
        long long rez;
        while ( alfa <= b )
        {
            for ( int i = b ; i >= poz ; i-- )
                if ( cmmmdc(alfa,i) == 1 )
                {
                    rez = i-alfa+1;
                    poz = i;
                    break;
                }
            if ( amax < rez )
                amax = rez;
            alfa++;
        }
        cout << amax;
    }
    return 0;
}