#include <iostream>
#include <fstream>

using namespace std;

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

long long n,i,j,prim;
short int ciur[2000001];

int main () {
    ciur[1]=1;
    f >> n;
    for (i=2;i<=n;i++)
        if (ciur[i]==0) {
            prim++;
            for (j=i+i;j<=n;j+=i) ciur[j]=1;
        }
    g << prim << '\n';
    f.close();g.close();
    return 0;
}