#include<stdio.h>

using namespace std;

long N,j,nr,i;
char v[2000005]

int main()

{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	scanf("%ld", &N);
	for(i=2;i<=N;i++)
		if(v[i]==0)
		{
			nr++;
			for(j=i+i;j<=N;j=j+i)
		       if(v[j]==0)
				   v[j]=1;
		}
		
	printf("%ld",nr);
    return 0;
}