#include <stdio.h>
#define Nmax 2000001
long N,i,j,S;
int ciur[Nmax];
int main () 
{
	FILE *f, *g;
	f=fopen("ciur.in", "r");
	fscanf(f, "%d", &N);
	fclose(f);
	g=fopen("ciur.out", "w");
	for (i=2; i<=N; i++)
		if (!ciur[i]) for (j=i+1; j<=N; j++) 
			if (j%i==0) ciur[j]=1;
	for (i=2; i<=N; i++)
		if (!ciur[i]) S++;
	fprintf(g, "%d", S);
	fclose(g);
	return 0;
}