#include <cstdio>
#include <cstdlib>
#include <iostream>

using namespace std;

const int N = 1000000;

int num[N];

void init() {
	num[0] = num[1] = 0;
	for (int i=2; i<N; ++i) num[i] = 1;
	for (int i=2; i<1000; ++i) {
		if (num[i * i]) {
			int j = i + i;
			for (;j < N; num[j] = 0, j += i); 
		}
	}
	for (int i=1; i<N; ++i) num[i] += num[i-1];
}

int main() {
	int n;
	init();
	while (scanf("%d", &n) != EOF) {
		printf ("%d\n", num[n]);
	}
	return 0;
}