#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;
using ll = long long;

int main()
{
    ll n, d, mod = -1, frac = 0, a;
    cin >> n >> d;
    mod = n % d;
    a = pow(n, 0.5);
    vector<ll> p(a+1, 1);
    p[0] = 0;
    p[1] = 0;
    for (int i = 2; i <= a; i++){
        if (p[i]) for (int j = i*i; j <= a; j += i) p[j] = 0;
    }
    if (!mod) cout << (n-1)/d << endl;
    else if (n == d) cout << 0 << endl;
    else if (!(d%mod)) {
        frac = d/mod;
        cout << n*frac/d - 1 << endl;
        return 0;
    } else {
        for (int i = 0; i <= max(d, mod); i++){
            if (!(d%p[i]) && !(mod%p[i])) {
                frac = p[i];
                cout << n*frac/d -1 << endl;
                return 0;
            }
        }
        cout << d -1 << endl;
    }
}