#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N = 1e7;
bool primes[N + 10];
int ans,n;
int init(){
	for(int i = 2 ; i <= n / i ; i ++)
		if(!primes[i])
			for(int j = i * i ; j <= n ; j += i) primes[j] = true;
}
signed main(){
	scanf("%lld",&n);
	init();
	for(int i = 2 ; i <= n ; i ++)
		if(primes[i] == false)
			ans++;
	cout << ans << endl;
	return 0;
}