#include<stdio.h>

long n,i,k;
char t[2000005];

int main()
{	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);	
	scanf("%ld",&n);
	k=0;
	for(i=2;i<=n;i++)
		t[i]=0;
	for(i=2;i<=n;i++)
		if(t[i]==0)
		{	k++;
			for(long j=i+i;j<=n;j+=i)
				t[j]=1;
		}
	printf("%ld",k);
	fclose(stdin);
	fclose(stdout);
	return 0;
	
}