#include<stdio.h>

#define M 2000001

int p[M];

int ciur(int N)
{
	int i,j=0,pr=0;
	for(i=2;i<=N;++i)
		if(p[i]==0)
			for(j=i+i;j<=N;j+=1)
				p[j]=1;
	for(;N>=2;--N)
		if(p[i]==0)
			++pr;
	return pr;
}

int main()
{
	int N;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&N);
	printf("%d\n",ciur(N));
	return 0;
}