#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
bool flg[N];
int n,sum;
signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	
	cin>>n;
	
	for(int i=2;i<=n;i++){
		if(i==1) continue;
		if(flg[i]) continue;
		else {
			sum++;
			for(int j=i+i;j<=N;j+=i){
				flg[j] = true;
			}
		}
	}
	cout<<sum;
	return 0;
}

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