#include <iostream>
#include <cstdio>
#include <vector>
#include <stack>
#include <algorithm>
#include <fstream>
using namespace std;
#define inf 0xfffffff

#define MAX 2000010
bool p[MAX];

void ciur() {
	int i = 2;
	while (i <= 1414) {
		while (p[i]) i++;
		for (int j = i * i; j < MAX; j += i) p[j] = 1;
		i++;
	}
}

int n, nr;

int main() {
	int a, b, c;
	
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	ciur();
	scanf("%d", &n);
	for (int i = 2; i <= n; i++) {
		if (!p[i]) nr++;
	}
	printf("%d\n", nr);
	
	return 0;
}