#include<stdio.h>
#include<vector>
#include<algorithm>
using namespace std;

// just chilling ( e admiterea la unibuc maine :p, si nu am mai codat de mult.. )

#define NMAX 2000004
bool P[NMAX];

int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	int N;
	scanf("%d",&N);
	
	int i,j;
	
	int SOL=1; // i=2 
	
	for(i=3; i<=N; i+=2)
	{
		if( !P[i] )
		{
			++SOL;
			for(j=i+i; j<=N; j+=i)
			{
				P[j]=1;
			}
		}
	}
		
	printf("%d\n",SOL);
	
	
	return 0;
}