#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>

using namespace std;

#define int long long
#define rep(i,n) for(int i = 0; i < (n); i++)
#define INF ((long long)1e18)
#define MOD ((int)1e9+7)
#define endl "\n"

#define yn(f) ((f)?"Yes":"No")
#define YN(f) ((f)?"YES":"NO")

#define MAX

#define MAX_PN  1010000

bool PN[MAX_PN];

void huga(int t, int x){
	if(PN[t]) return;
	for(int i = t*t; i <= x; i+=t)
		PN[i] = true;
}

void Sieve_of_Eratosthenes(int x){
	PN[0]=PN[1]=PN[4]=true;
	for(int i = 6; (i-1)*(i-1) <= x; i+=6)
		huga(i-1,x),huga(i+1,x);
	for(int i = 6; i <= x; i+=6)
		PN[i]=PN[i+2]=PN[i+3]=PN[i+4]=true;
}

signed main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);
	
	int N, P;
	
	int ans = 0, con = 0;
	
	cin>>N>>P;
	
	Sieve_of_Eratosthenes(N+1);
	
	for(int i = N/2 + 1; i <= N; i++){
		if(PN[i] == true) con++;
		// cout<<"i = "<<i<<endl;
	}
	
	
	// cout<<N/2 - 1<<" "<<con<<sendl;
	con = N/2 - 1 + con;
	
	if(P == 1){
		cout<<1<<endl;
	} else if(P <= N/2){
		cout<<con<<endl;
	} else if(PN[P] == true){
		cout<<con<<endl;
	} else if(PN[P] == false){
		cout<<1<<endl;
	}
	
	return 0;
}