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

int n,i,j,c=0;
char v[2000001];
int main() {


    ifstream f ("ciur.in");
    ofstream g ("ciur.out");

    f>>n;

    for (i=2;i<=n;i++) {
        if (v[i]==0) {
            c++;
            for (j=i;j<=n;j+=i) {
                v[j]=1;
            }
        }
    }
    g<<c;
    return 0;
}