Program NN;
Uses crt;
Var n,i,d: longint;
Function ngto(a: longint): boolean;
Var i: longint;
Begin
If a<2 then exit(false);
For i:=2 to trunc(sqrt(a)) do
If a mod i = 0 then exit(false);
exit(true);
End;
Begin
Clrscr;
Write('Nhap n: '); Readln(n);
d:=0;
For i:=1 to n do
If ngto(i) then inc(d);
Write('D = ',d);
Readln
End.