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

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

bool v[2000100];
int N, i, j, S;

int main()
{

    f>>N;

    for(i=1;i<=N; i++)
        v[i] =1;

    for (i=2;i<=N;i++)
        if(v[i]==1)
           for(j=2;j*i<=N;j++)
               v[i*j]=0;

  for(i=1;i<=N;i++)
     if(v[i]==1)
        S+=1;
    g<<S-1;
}