#include<stdio.h>
#define M 2000005
long n,c[M],r;
FILE*f=fopen("ciur.in","r");
FILE*g=fopen("ciur.out","w");
int main()
{long i,j;
 fscanf(f,"%ld",&n);
 for(i=2;i<=n;i++)
	c[i]=1;
 for(i=2;i<=n;i++)
	{if(c[i]) {r++;
		   for(j=i;j<=n;j+=i)
			c[j]=0;}}
 fprintf(g,"%ld",r);
 fcloseall();
 return 0;
}