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