#include <iostream>
#include <fstream>
#include <math.h>
 
using namespace std;
 
ifstream in("ciur.in");
ofstream out("ciur.out");
 
int main()
{
    int N;
	int a[200000];
    in>>N;
     
    for(int i = 0 ; i <= N ; i++)
        a[i] = i;
    for(int i = 2 ; i <= (int)sqrt((float)N); i++)
		for(int j = i * 2 ; j <= N ; j = j + i)
                a[j] = 0;
    int count = 0;
    for(int i = 2 ; i <= N ; i++)
		if(a[i] != 0) count++;
    out<<count;
    return 0;
}