Методом Рунге-Кутта найти решение дифференциальных уравнений

VAR
 Xbef,Ybef,Xaft,Yaft,H,K1,K2,K3,K4:Real;
 i,N:Word;

Function F(Xf,Yf:Real):Real;
begin
 F:=Yf-Xf;
end;

Function fK1(Xk,Yk:Real):Real;
begin
 fK1:=F(Xk,Yk);
end;

Function fK2(Xk,Yk,Hk:Real):Real;
begin
 fK2:=F(Xk+Hk/2,Yk+Hk/2*fK1(Xk,Yk));
end;

Function fK3(Xk,Yk,Hk:Real):Real;
begin
 fK3:=F(Xk+Hk/2,Yk+Hk/2*fK2(Xk,Yk,Hk));
end;

Function fK4(Xk,Yk,Hk:Real):Real;
begin
 fK4:=F(Xk+Hk,Yk+Hk*fK3(Xk,Yk,Hk));
end;

Function Y_acc(X_acc:Real):Real;
begin
 Y_acc:=0.5*Exp(X_acc)+X_acc+1;
end;

BEGIN
 H:=0.1;
 N:=Round(1/H);
 Xbef:=0;
 Ybef:=1.5;
 WriteLn(' X           Y             Y_accur');
 Writeln(Xbef:4:2,Ybef:15:5, Y_acc(Xbef):15:5);
 For i:=1 to N do
  begin
   Xaft:=Xbef+H;
   K1:=fK1(Xbef,Ybef);
   K2:=fK2(Xbef,Ybef,H);
   K3:=fK3(Xbef,Ybef,H);
   K4:=fK4(Xbef,Ybef,H);
   Yaft:=Ybef+H/6*(K1+2.0*K2+2.0*K3+K4);
   Writeln(Xaft:4:2,Yaft:15:5, Y_acc(Xaft):15:5);
   Xbef:=Xaft;
   Ybef:=Yaft;
  end;
 ReadLn;
END.