#include <iostream>

using namespace std;

int Euclid(int x, int y)
{
    int r;
    while (y)
    {
        r=x%y;
        x=y;
        y=r;
    }
    return x;
}

int main()
{
    long long a,b,dm=0, am,bm, gasit=0;
    cin>>a>>b;
    if (Euclid(a,b)==1)
        cout <<b-a+1;
    else
    {
        for (int i=1; i<4 && gasit==0; i++)
        {
            if (Euclid (a+i,b)==1)
            {
                dm=b-a-i+1;
                gasit=1;
            }
        }
        gasit=0;
        for (int i=1; i<4 && gasit==0; i++)
        {
            if (Euclid (a,b-i)==1)
            {
                if(dm>b-i-a+1)
                    dm=b-i-a+1;
                gasit=1;
            }
        }
        cout<<dm;
    }

    return 0;
}