#include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <string>
using namespace std;

#define rep(i,n) for(int i=0;i<int(n);i++)

bool prime[1000000];
int cou[1000000]={0};

int main(){
	int n;
	
	rep(i, 1000000) prime[i] = true;
	prime[1]=false;
	for(int i=1;i*i<1000000;i++){
		if(prime[i]){
			for(int j=i*i;j<1000000;j+=i){
				prime[j]=false;
			}
		}
	}
	rep(i,999999){
		if(prime[i+1]) cou[i+1]=cou[i]+1;
		else cou[i+1]=cou[i];
	}
	while(cin>>n){
		cout<<cou[n]<<endl;
	}
	return 0;
}