#include "bits/stdc++.h"
using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define array2(type, x, y) array<array<type, y>, x>
#define vector2(type) vector<vector<type> >
#define out(...) printf(__VA_ARGS__)

int dxy[] = {0, 1, 0, -1, 0};

void solve();
signed main()
{
#if DEBUG
    std::ifstream in("input.txt");
    std::cin.rdbuf(in.rdbuf());
#endif
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}

/*================================*/

int N,P;

void solve() {
    cin>>N>>P;
    
    if(P==1) {
        cout << N << endl;
        return;
    }
    
    set<int> primes;
    primes.insert(2);
    FOR(i,3,1e6) {
        bool ng = false;
        for (auto p:primes) {
            if (p*p>i) break;
            if (i%p==0) {
                ng=true;
                break;
            }
        }
        if (ng) continue;
        primes.insert(i);
    }
    if (P > N/2) {
        if (primes.count(P))  {
            cout << 1 << endl;
            return;
        }
    }
    
    int ans = N-1;
    FOR(i,N/2+1,N+1) {
        if (primes.count(i)) ans--;
    }
    
    cout << ans << endl;
}