CONST
 Eps=0.0001;
VAR
 Xbeg,Xfin,DX,SUM,X:REAL;
 N:WORD;
 Nx,i:INTEGER;

FUNCTION ArcCos(Xa:Extended):Extended;
 begin
  if ROUND(Xa*10000000)=10000000 then ArcCos:=0 else
  if ROUND(Xa*10000000)=-10000000 then ArcCos:=Pi else
  ArcCos:=(Pi/2)-ArcTan(Xa/SQRT(1-Xa*Xa));
 end;


PROCEDURE SUMS(Xs:REAL; Var S:REAL; Var Ns:WORD);
 VAR
   a:REAL;
 Begin
  a:=Xs;
  S:=Xs;
  Ns:=0;
  Repeat
   Inc(Ns);
   a:=a*SQR(Xs)*(2*Ns-1)*(2*Ns-1)/(2*Ns)/(2*Ns+1);
   S:=S+a;
  Until Abs(a)<Eps;
  S:=Pi/2-S;
 End;

BEGIN
 Write('Xbeg= ');
 ReadLn(Xbeg);
 Write('Xfin= ');
 ReadLn(Xfin);
 Write('DX= ');
 ReadLn(DX);
 WriteLn;
 WriteLn('         Results of calculation:');
 WriteLn('    X          SUM         N    ArcCos(X)');
 WriteLn;
 Nx:=ROUND((Xfin-Xbeg)/DX);
 X:=Xbeg;
 For i:=0 to Nx do
  begin
   X:=Xbeg+DX*i;
   SUMS(X,SUM,N);
   WriteLn(X:8:5,'     ',SUM:7:5,'     ',N:3,'     ',ArcCos(X):7:5);
  end;
 ReadLn;
END.