#include<fstream>

using namespace std;

#define MAX 2000001
bool isPrime[MAX];

int main(){
ifstream in; ofstream out;
in.open("ciur.in"); out.open("ciur.out");
out.clear();

int n,i,j,no=0;

in>>n;
for(i=2;i<=n;i++){
  if(isPrime[i]==0){
     no++; 
     for(j=i*i;j<=n;j=j+i) isPrime[j]=1; 
  }
}

out<<no;
in.close(); out.close();
return 0;
}