#pragma region
#pragma GCC target("avx2")
#pragma GCC optimize("03")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std; typedef long double ld; typedef long long ll;
typedef unsigned long long ull;
#define endl "\n"
#define FOR(i,a,b) for(int i=(a);i<=(b);i++)
#define rep(i,n) for(int i=0;i<(n);i++)
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define ALL(x) (x).begin(), (x).end()
constexpr int INF=1<<30; constexpr ll LINF=1LL<<60; constexpr ll mod=1e9+7; constexpr int NIL = -1;
template<class T>inline bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>inline bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }
#pragma endregion
//-------------------

map<int,int> factorize(int n) {
    map<int, int> ans;
    for(int i=2;i*i<=n;i++) {
        while(n%i==0) {
            ans[i]++;
            n /= i;
        }
    }
    if(n!=1) ans[n]++;
    return ans;
}

vector<bool> prime(int n) {
    vector<bool> isprime(n+1, true);
    isprime[0] = false;
    isprime[1] = false;
    for(int i=2;i<=n;i++) {
        if(!isprime[i]) continue;
        for(int j=i+i; j<=n; j+=i) isprime[j] = false;
    }
    return isprime;
}

int main(){
    cin.tie(0); ios::sync_with_stdio(false); //cout << fixed << setprecision(15);
    int n,p; cin >> n >> p;
    
    if(p==1) {
        cout << 1 << endl;
        return 0;
    }

    auto isprime = prime(n);
    if(isprime[p] and n==p) {
        cout << 1 << endl;
        return 0;
    }
    int ans = 1;
    for(int i=n/2+1; i<=n; i++) 
    {
        // cout << i << endl;
        ans += isprime[i];
    }
    cout << n-ans << endl;
    return 0;
}