#include <bits/stdc++.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
#define cin f 
#define cout g 
const int Max = 2e6 + 1;

int n, ans;
bool prim[Max];
int main()
{
	cin >> n;
	for(int i=1;i<=n;i++)
		prim[i] = true;
	for(int i=2;i*i<=n;i++)
		if(prim[i] == true)
			for(int j=i*i;j<=n;j+=i)
				prim[j] = false;
	for(int i=2;i<=n;i++)
		if(prim[i] == true)
			ans ++;
	cout << ans;
	return 0;
}