program ural1070;
var
  a,b,c,d:real;
begin
  readln(a,b);
  readln(c,d);
  a:=trunc(a)+frac(a)/60*100;
  b:=trunc(b)+frac(b)/60*100;
  c:=trunc(c)+frac(c)/60*100;
  d:=trunc(d)+frac(d)/60*100;
  a:=b-a;
  if a<=-12 then a:=a+24;
  if a>=12 then a:=a-24;
  c:=d-c;
  if c<=-12 then c:=c+24;
  if c>=12 then c:=c-24;
  writeln(round(abs(a-c)/2));
end.