/*
    Keep It Simple!
*/

#include<stdio.h>
#include<list>

using namespace std;

#define MaxN 2000005

bool Era[MaxN];
int N,Prime;

int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);

	scanf("%d",&N);

	Prime = 1;
	for(int i=3; i<=N; i+=2)
	{
		if(!Era[i])
		{
			Prime++;
			for(int j=i; j<=N; j+=i)
			    Era[j] = 1;
		}
	}

	printf("%d",Prime);
}