#include <bits/stdc++.h>
using ll=long long;
#define S second
#define F first
#define endl '\n'
#define spid ios_base::sync_with_stdio(false);cin.tie(NULL);
const int mod=1e9+7;
const double pi=3.14159265359;
const int maxn=2000001;
using namespace std;

int n;
char A[maxn];

int main(){
	ifstream cin("ciur.in");
	ofstream cout("ciur.out");
	cin>>n;
	for(int i=2;i*i<=n;i++){
		for(int j=i*i;j<=n;j+=i)A[j]=1;
	}
	int cnt=0;
	//for(int i=2;i<=n;i++)cout<<A[i]<<" ";
	for(int i=2;i<=n;i++)if(A[i]==0)cnt++;
	cout<<cnt<<endl;
}