#include<iostream>
#include<iomanip>
#include<string>
#include<algorithm>
#include<functional>
#include<vector>
#include<math.h>
#define L(_i,_N) for(int _i=0;_i<_N;_i++)
#define C(_Dis) cout<<_Dis<<endl;

using namespace std;

typedef long long int lli;

int main() {
	int n,Count=0;
	while (cin >> n) {
		vector<bool> ch(n+1);
 		for (int i = 2; i <= n; i++) ch[i] = true;
		for (int i = 2; i <= n; i++) {
			if (ch[i]) Count++;
			for (int j = i * 2; j <= n; j += i) ch[j] = false;
		}
		C(Count);
		Count = 0;
	}
	return 0;
}