#include<stdio.h>

int main()
{
	int n,i,j,nr=0;
	char prime[2000001];
	FILE *f=fopen("ciur.in","r");
	fscanf(f,"%i",&n);
	fclose(f);

	for(i=0;i<=2000000;i++)
		prime[i]=1;
	for(i=2;i<=n;i++)
	{
		if(prime[i]==1)
		{
			for(j=i+i;j<=n;j+=i)
				prime[j]=0;
			nr++;
		}
	}
	f=fopen("ciur.out","w");
	fprintf(f,"%i\n",nr);
	fclose(f);
	return 0;
}