#include <iostream>
#include <algorithm>
#include <fstream>
#include <cmath>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int v[2000005];
int main()
{
int n,c=0;
fin >>n;
int sqrt_n=sqrt(n);
for (int i=2;i<=sqrt_n;++i)
{if (v[i]==1) {continue;}
    for (int j=i+i;j<=n;j+=i) v[j]=1;

}
for (int i=2;i<=n;i++) if (v[i]==0) c++;
fout << c;
}