#include <stdio.h>
#include <bitset>

using namespace std;

bitset<2000001> bt;
int n;


int ciur()
{
	for (int i=2;i*i<=n;++i)
		if (bt[i]==0)
			for (int j=i*i;j<=n;j+=i)
				bt[j]=1;
  
  int count=0;

  for (int i=2;i<=n;++i)
  	if (bt[i]==0) 
  		count++;

  return count;

}

int main(int argc, char const *argv[])
{
	 fscanf(fopen("ciur.in","r"),"%d",&n);
	 fprintf(fopen("ciur.out","w"),"%d",ciur());
	return 0;
}