#include <iostream>
#include <fstream>
using namespace std;

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