#include <fstream>
#include <math.h>

using namespace std;

bool v[2000001];

int main(){

    ifstream in ("ciur.in");
    ofstream out ("ciur.out");
    long long n,S;
    S=0;
    in>>n;
  for(int i=2;i<2000000;i++)
        if(v[i]==0){
            if(i<=n)
                S++;
        for(int j=i+i;j<=2000000;j=j+i)
        v[j]=1;}
    out<<S;
    in.close();
    out.close();
    return 0;
}