#include<fstream.h>
#define NM 2000000

int main(){

char v[NM+1]={0};
int i,j,n,p;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
fin>>n;
v[1]=1;
for(i=2;i<=n/2;i++)
	if(v[i]==0)
	   for(j=2;j*i<=n;j++)
			  v[i*j]=1;
p=0;
for(i=2;i<=n;i++)  if(v[i]==0) p++;
fout<<p;
return 0;
}