#include<iostream>
#include<fstream>
#define NMAX 2000000
#include<stdio.h>
#include<math.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,v[NMAX];

int main()
{int i,j,k=0;
	f>>n;

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

	


for(i=2;i<=n;i++)
		if(v[i]==0)k++;
g<<k;
return 0;
}