#include <stdio.h>

int ciur[20000001];
long int n, i, j, k;
int nr;

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