#include <iostream>
#include <cmath>

int main(){
	using namespace std;
	while(1){
		int n,i,j=2,count = 0;
		cin >> n;
		if (cin.eof() || n == 0) break;
		int prime[n+1];
		for(i=2;i<=n;i++) prime[i] = 1;
		for(i=2;i<=n;i++){
			if(prime[i] == 0) continue;
			else{
				for(j=2*i;j<=n;j++){
					if(j%i == 0) prime[j] = 0;
				}
			}
		}
		for(i=2;i<=n;i++){
			if(prime[i] == 1) count += 1;
		}
		cout << count << endl;
	}
	return 0;
}