#include "stdio.h"

int N;
char a[2000001];

int main () {
	int i, c=0;
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	scanf("%d", &N);

	for (i = 2; i <= N; ++i)
		a[i]=1;
	for (i = 2; i <= N; ++i) 
		if (a[i]) {
			c++;
			for (int j = i+i; j < N; j+=i)
				a[j]=0;
}
					
	
	printf("%d\n", c);

	return 0;

}