#include<iostream>
#include<cstdio>

using namespace std;

int ciur(const int& N)          // int ciur(int number)
{
	int nrOfPrimes = 0;
	bool a[2000005];
	for(int i = 2 ; i <= N ; i++)
		a[i] = 1;
	for(int i = 2 ; i <= N ; i++)
	   if(a[i] == 1)
	   {
			nrOfPrimes++;
	 		for(int j = (i<<1) ; j <= N ; j = j+i)
				a[j] = 0;
	   }
	return nrOfPrimes;
}

int main()
{
	int number;
	FILE *in,*out;
	in = fopen("ciur.in","r");
	out = fopen("ciur.out","w");
	fscanf(in,"%d",&number);
	fprintf(out,"%d",ciur(number));
	fclose(in);
	fclose(out);
	return 0;
}