#include <fstream>
#include <string.h>
#include <iostream>
#include <cstdlib>
#include <stack>
#include <math.h>
using namespace std;
char nums[2000005];
int main(){
	
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	int number, i, j, sum = 0;
	fin>>number;
	for(i = 2; i <= number; i++){
		if(nums[i] == 0){
			sum++;
			for(j = 2*i; j <= number; j+=i){
				nums[j] = -1;
			}
		}
	}
	fout<<sum;
	return 0;
}