// ciurul lui Eratostene
#include <stdio.h>
bool prim[2000000];

int main()
{
	long n,i,j,nr=0;

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

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

	for (i=2;i<=n;i++)
	{
		if (prim[i]==0)
		{
			nr++;
			for (j=i+i;j<=n;j+=i)
				prim[j]=1;
		}
	}

	fprintf(g,"%d\n",nr);

	fclose(f);
	fclose(g);
	
	return 0;
}