#include <iostream>

using namespace std;

long long a, b;

long long gcd(long long a, long long b){
    if(!b)
        return a;
    return gcd(b, a % b);
}

int main(){
    cin >> a >> b;
    while(gcd(a, b) != 1 && a != b)
        ++a;
    if(a == b)
        a += 2;
    cout << b - a + 1;
    return 0;
}