#include<bits/stdc++.h> using namespace std; const int N = 50000010; bool isp[N]; vector prime; void eulerPrime(int n) { memset(isp, true, sizeof(isp)); isp[0] = isp[1] = false; for (int i = 2; i <= n; i++) { if (isp[i]) prime.push_back(i); for (int p : prime) { if (i * p > n) break; isp[i * p] = false; if (i % p == 0) break; } } }

int main(){ int n; cin>>n;

eulerPrime(n);
cout<<prime.size();
return 0;

}