#include<stdio.h>

FILE *in,*out;

//constante
const int Nmax=(int)2e6+5;

//varibile
int n,answer;
bool notPrime[Nmax];

int main(void)
{
	in=fopen("ciur.in","rt");
	out=fopen("ciur.out","wt");
	fscanf(in,"%d",&n);
	
	for(int i=2; i<=n; ++i)
	{
		if(!notPrime[i])
		{
			++answer;
			for(int j=i+i; j<=n; j+=i)
				notPrime[j]=true;
		}	
	}	
	fprintf(out,"%d\n",answer);
	fclose(in);
	fclose(out);
	return 0;
}