#include <cstdio>
#define Nmax 2000002
using namespace std;

int n;
int ct = 0;
char pr[Nmax];	// 0 - prim, 1 - neprim

int main()
{
	FILE *g = fopen("ciur.in", "r");
	fscanf(g, "%d", &n);
	fclose(g);
	
	for (int i = 2; i <= n; i++)
		if (!pr[i])
		{
			//printf("%d ", i);
			ct++;
			for (int j = i+i; j <= n; j += i)
				pr[j] = 1;
		}
	g = fopen("ciur.out", "w");
	fprintf(g, "%d", ct);
	return 0;
}