VAR
 a,b,c,d:ShortInt;
BEGIN
 write('a= ');
 readln(a);
 write('b= ');
 readln(b);
 write('c= ');
 readln(c);
 write('d= ');
 readln(d);
 If ((c=a-1) or (c=a+1)) and (d=b-1) then
  WriteLn('YES!')
 else
  WriteLn('NO!');
 Readln
END.

VAR
 a,b,x:Real;
BEGIN
 write('a= ');
 readln(a);
 write('b= ');
 readln(b);
 If a>0 then WriteLn('x < ',-b/a)
 else
 If a<0 then WriteLn('x > ',-b/a)
 else WriteLn('No solution!');
 Readln
END.

VAR
 g,m,n,g1,m1,n1:Word;
BEGIN
 write('g= ');
 readln(g);
 write('m= ');
 readln(m);
 write('n= ');
 readln(n);
 If (m=1) and (n=1) then
  begin
   g1:=g-1;
   m1:=12;
   n1:=31;
  end
 else
  begin
   g1:=g;
   If n>1 then
    begin
     m1:=m;
     n1:=n-1;
    end
   else
    begin
     m1:=m-1;
     Case m of
      2,4,6,8,9,11: n1:=31;
      5,7,10,12: n1:=30;
      else
       begin
        if (((g mod 4)=0) and ((g mod 100)>0)) or
           (((g mod 4)=0) and ((g mod 400)=0)) then n1:=29
        else n1:=28;
       end;
     end; { Case }
    end;
  end;
 WriteLn('Previous date is ',n1,'.',m1,'.',g1);
 Readln
END.

VAR
 i,n:WORD;
 Sum:Real;
BEGIN
 Write('n= ');
 ReadLn(n);
 Sum:=0;
 For i:=1 to n do
  Sum:=Sum+1/i;
 WriteLn('Sum= ',Sum);
 ReadLn
END.