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

int main()
{
    int N;
	int a[2000000];
    in>>N;
	
    for(int i = 2 ; i <= (int)sqrt((float)N); i++)
		for(int j = i * 2 ; j <= N ; j = j + i)
                a[j] = 1;
    int count = 0;
    for(int i = 2 ; i <= N ; i++)
		if(a[i] == 0) count++;
    out<<count;
    return 0;
}