// ciurul lui Eratostene

#include <stdio.h>

int ciur(int n)
{
	int i,j,nr=0,prim[250000];

	for (i=2;i<=n;i++)
	{
		if (prim[i])
		{
			nr++;
			for (j=i+i;j<=n;j+=i)
				prim[j]=0;
		}
	}
	
	return nr;
}

int main()
{
	int n;

	FILE* f=fopen("ciur.in","rt");
	FILE* g=fopen("ciur.out","wt");

	fscanf(f,"%d", &n);

	fprintf(g,"%d",ciur(n));

	fclose(f);
	fclose(g);

	return 0;
}