Program gfsd;
Var s,w:String;
x,d:Byte;
Begin
Write('Vvedite stroky'); Readln(s);
w:='';
x:=2;
While x d:=2;
While (x Mod d<>0) And (d<=Sqrt(x)) Do
d:=d+1;
If d>Sqrt(x) Then w:=w+s[x];
x:=x+1
End;
Writeln(w)
End.