/*
	大号水?，拿来?手
*/
#include<iostream>
#include<string.h>
#include<string>
#include<stdio.h>
#include<math.h>
#include<algorithm>
using namespace std;

int Find_Number (int x)
{
	int cnt = 0;
	for (int i=2;i<=x;i++)
	{
		bool flag = false;
		for (int j=2;j<=sqrt((double)i);j++)
		{
			if ( i % j == 0)
			{
				flag = true;
				break;
			}
		}
		if (flag == false )
		{
			cnt++;
		}
	}
	return cnt;
}

int main ()
{
	int N;
	scanf("%d",&N);
	cout<<Find_Number (N)<<endl;
	return 0;
}