Program pi_wallis;
Var p, r, diff : real;
i : longint;
Begin
p:=1;
i:=0;
Repeat
i:=i+2;
r:=i/(i-1)*i/(i+1);
diff:= (p*r) - p;
p:=p*r;
Until abs (diff) < 1e-8;
Writeln ('par la formule de wallis pi = ', 2*p:2:7);
End.