#include<cstdio>
#include<iostream>
#include<cmath>
#include<string>
#include<cstring>
#include<algorithm>
using namespace std;
bool ans[100000005];
int main(){
	memset(ans,1,100000005*sizeof(bool));
	int n,sum=0;
	cin>>n;
	ans[1]=0; 
	for(int i=2;i<=n;i++){
		if(ans[i]==true){
			for(int j=i*i;j<=n;j+=i){
				//cout<<j<<' ';
				ans[j]=false;
		 }	
		}
	} 
	for(int i=2;i<=n;i++){
		if(ans[i]==true)
		sum++;
	}
	cout<<sum;
    return 0;
}