#include<stdio.h>
long int n,i,j,nr;
FILE *in=fopen("ciur.in","r");
FILE *out=fopen("ciur.in","w");
int main()
{
char p[2000001];
fscanf(in,"%ld",&n);
for(i=1;i<=n;i++) p[i]=0;
for(i=2;i<=n;i++)
	{
	if(p[i]==0)
		{
		nr++;
		for(j=i*i;j<=n;j+=i)
			{
			p[j]=1;
			}
		}
	}
fprintf(out,"%ld",nr);
return 0;
}