#include<stdio.h>

FILE *in,*out;

//definitions

//constants
const int sz = (int) 2e6+1;

//variables
int number;
bool notPrime[sz];
int answer;

//functions

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