#include<fstream.h>
#define NN 2000000
int main(){

char v[NN+1]={0};
int i,j,n,p;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
fin>>n;
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;
}