#include<bits/stdc++.h>
using namespace std;

const int N = 2000009;
bool composite[N];

//ifstream in ("ciur.in");
//ofstream out("ciur.out");
auto& in = cin;
auto& out = cout;

int main(){
	int n, count = 0;
	in>>n;
	for(int i=2;i<=n;i++)
		if(!composite[i]) {
			count++;
			for(int j=2*i;j<=n;j+=i)
				composite[j] = true;	
		}
	out<<count<<endl;
	return 0;
}