#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <climits>
#include <limits>
#include <ctime>
#include <cstring>
#include <string>
#include <sstream>
#include <cstdlib>
#include <iomanip>

using namespace std;

const int N = 100000000 + 5;
int n;
int cnt = 0;
bool vis[N];

void ass() {
	register int i, j;
	for (i = 2; i <= n; ++i) {
		if (vis[i] == 0) {
			++cnt;
			for (j = i * i; j <= n; j += i) {
				vis[j] = 1;
			}
		}
	}
	return ;
}

int main() {
	register int i, j;
	scanf("%d", &n);
	ass();
	printf("%d\n", cnt);
	return 0;
}