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


  fout<<cnt;
  return 0;
}