#include #include using namespace std; #define DEBUG(x) cerr<<#x<<": "< #define vl vector #define vii vector< vector > #define vll vector< vector > #define vs vector #define pii pair #define pis pair #define psi pair #define pll pair template pair operator+(const pair &s, const pair &t) { return pair(s.first + t.first, s.second + t.second); } template pair operator-(const pair &s, const pair &t) { return pair(s.first - t.first, s.second - t.second); } template ostream& operator<<(ostream& os, pair p) { os << "(" << p.first << ", " << p.second << ")"; return os; } #define X first #define Y second #define rep(i,n) for(int i=0;i<(n);i++) #define rep1(i,n) for(int i=1;i<=(n);i++) #define rrep(i,n) for(int i=(n)-1;i>=0;i--) #define rrep1(i,n) for(int i=(n);i>0;i--) #define REP(i,a,b) for(int i=a;i bool chmax(T &a, const T &b) { if (a bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; } #define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end()); const ll inf = 1000000001; const ll INF = (ll)1e18 + 1; const ll MOD = 1000000007; //const ll MOD = 998244353; const double pi = 3.14159265358979323846; #define Sp(p) cout<> n >> p; vector prime(n + 1, true); prime[0] = prime[1] = false; rep (i, n + 1) { if (prime[i]) { for (int j = 2; i*j <= n; j++) { prime[i*j] = false; } } } if (p == 1 || (prime[p] && p > n / 2)) { cout << 1 << endl; return 0; } int cnt = 0; for (int i = n / 2 + 1; i <= n; i++) { cnt += prime[i]; } cout << n - cnt - 1 << endl; }