#include <iostream>
#include <fstream>
#include <bitset>

using namespace std;

const int N=2000000;

bitset <N+1> c;

int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n;
    fin>>n;
    int counter=0;
    
    for(int i=2;i*i<=n;i++){
        if(!c[i]){
            for(int j=i*i;j<=n;j+=i){
                c[j]=1;
            }
        }
    }
    for(int i=2;i<=n;i++){
        if(c[i]==0){
            counter++;
        }
    }
    fout<<counter;
    return 0;
}