#include <stdio.h>

FILE *f;
FILE *g;

int n, i, nr, y, j;
char x[2000001];

void citire()
{
	f=fopen("ciur.in", "r");
	fscanf(f, "%d", &n);
	fclose(f);
}

void prelucrare()
{
	g=fopen("ciur.out", "w");
	
	for(i=2;i<=n;i++)
	{
		if(x[i]==0)
		{	
			y=i+i;
			while(y<=n)
			{
				x[y]=1;
				y=y+i;
			}
		}
	}
	for(i=2;i<=n;i++)
		if(x[i]==0)
			nr++;
	fprintf(f, "%d", nr);
	fclose(g);

}

int main()
{
	citire();
	prelucrare();
	return 0;
}