#include<stdio.h>

char a[2000001];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    int n,i,j,gh=0,k;
	scanf("%d", &n);

	for(i=2;i<=n;++i)
	{
		if(a[i]==0)
		{
			++gh;
			k=2;
			j=i*k;
			while(j<=n)
			{
				a[j]=1;
				++k;
				j=i*k;
			}
       }
   }
   printf("%d",gh);
   return 0;
}