#include<fstream.h>
int ok[2000];
int main()
{unsigned long n,i,j,k;

ifstream f("ciur.in");
ofstream g("ciur.out");

f>>n;
for(i=1;i<=n;i++)ok[i]=1;

for(i=2;i*i<=n;i++)
   if(ok[i]==1)
     {j=2;
      while(i*j<=n){ok[i*j]=0;
		    j++;
		    }
      }
     
k=0;
for(i=2;i<=n;i++) if(ok[i]==1)k++; 
g<<k<<'\n';

f.close();
g.close();
return 0;
}