#include <bits/stdc++.h>
using namespace std;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N, P;
    cin >> N >> P;
    if (P == 1){
        cout << 1 << endl;
        return 0;
    }
    vector<int> prime(N + 1, 1);
    prime[0] = 0;
    prime[1] = 0;
    for (int p = 2; p * p <= N; ++p){
        if (prime[p] == 0) continue;
        for (int pp = p * p; pp <= N; pp += p) prime[pp] = 0;
    }
    int min_p = P;
    for (int p = 2; p <= P; ++p){
        if (P % p == 0 and prime[p] == 1){
            min_p = p;
            break;
        }
    }
    if (min_p * 2 <= N){
        int rev = 1;
        for (int i = N/2 + 1; i <= N; ++i) rev += prime[i];
        cout << (N - rev) << endl;
    }else{
        cout << 1 << endl;
    }
    return 0;
}