#include <bits/stdc++.h>
using namespace std;

/* {{{ */
#define PI(N) ((M_PI * (N)) / 180) //?§???????????????¢??????????????????
#define CL(N) (cout << (N) << endl)
#define DCT(N) (cout << "debug " << (N) << endl)
#define REP(i, N) for (int i = 0; i < (N); i++)
/* }}} */

bool f[1000001] = {false};

int main()
{
	for (int i = 2; i * i < 1000001; i++){
    	for (int j = i * i; j < 1000001; j += i){
            f[j] = true;
        }
    }

	int n;
    while (cin >> n){
        int c = 0;
        for (int i = 2; i <= n; i++){
            if (!f[i])c++;
        }
        CL(c);
    }

	return (0);
}