#include <iostream>
#include "stdio.h"
#include "string.h"
#include "math.h"

using namespace std;

bool isPrime[100000000];
int main() {
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	int n, k = 0;
	scanf("%d", &n);
	memset(isPrime, true,sizeof(bool) * n);
	for(int i = 2; i <= n;i++){
		if(isPrime[i]){
			k++;
			for(int j = i + i; j <= n;j += i)
				isPrime[j] = 0;
		}
	}
	printf("%d", k);
	return 0;
}