#include <cstdio>
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <cmath>
#define rep(i,a,n) for(int i=a;i<n;i++)
using namespace std;

int main(void){
	int i,j,k,n,a;
	while(cin >> n){
		a=1;
	if(n==1){
		cout << "0\n";
	}
	else{
		for(i=3;i<=n;i+=2){
			k=0;
			for(j=3;j<=sqrt(i);j+=2){
				if(i%j==0){
					k=1;
					break;
				}
			}
	
			if(k==0) a++;
		}
	}

	printf("%d\n",a);
	}
	return 0;
}