#include<stdio.h>
#define N 2000008

int c[N];
int n;

void ciur()
{
	int i,j;
	for(i=2;i*i<=n;++i)
		if(c[i]==0)
			for(j=i*i;j<=n;j+=i)
				c[j]=1;
}

int main()
{
	int count=0;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	ciur();
	for(int i=2;i<=n;++i)
		if(c[i]==0)
			count++;
	printf("%d",count);
	return 0;
}