#include<stdio.h>
#define FIN "ciur.in"
#define FOUT "ciur.out"
#define N 2000001
char v[N];
int n;

void citire()
	{
	freopen(FIN,"r",stdin);
	scanf("%d ",&n);
	}

void ER()
	{
	int i,j,sol=0;
	for(i=2;i<=n;i++)
	v[i]=1;
	for(i=2;i<=n;i++)
	if(v[i])
		{
		sol++;
		for(int j=i;j<=n;j+=i)
		v[j]=0;
		}
	freopen(FOUT,"w",stdout);
	printf("%d\n",sol);

	}

int main()
	{
	citire();
	ER();
	return 0;
	}