#include <iostream>
#include <cstdio>

using namespace std;

char pr[2000001];
long N,cnt;

int main() {
	
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	
	scanf("%ld",&N);
	
	for (long i=2;i<=N;++i) pr[i] = 1;
	for (long i=2;i<=N;++i) {
		if (pr[i]) {
			cnt++;
			for (long j=i+i;j<=N;j+=i) pr[j] = 0;
		}
	}
	
	printf("%ld",cnt);
	
	fclose(stdin);
	fclose(stdout);
	
	return 0;
}