#include <iostream>
#include <fstream>
#include <math.h>
 
using namespace std;
 
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
    int N, count = 1, a[2000001];
    in>>N;
	
	for(int i = 4 ; i <= N ; i++)
		a[i] = 1;
	for(int i = 3 ; i <= N ; i+=2)
		if(a[i] == 0)
		{
			count++;
			for(int j = i ; j <= N ; j++)
				a[i] = 1;
		}
    out<<count;
    return 0;
}