Before sending solution, just test it on this examples.
1) 23.42 01.14
   08.10 17.51
Answer: 4
2) 01.01 10.59
   04.23 04.22
Answer: 5
3) 12.00 15.00
   01.02 03.07
Answer: 0
4) 23.58 00.43
   22.27 03.10
Answer: 2
5) 12.00 15.00
   20.00 21.00
Answer: 1
6) 01.01 21.59
   04.23 11.22
Answer: 5

;)

Thank you very much!!!!
I've got AC!!
HAHA!!

The test 3 is wrong.

Thank you  for others

Thanks a lot! It helps me very much.

I don't usually plan before writing a program, so I made lots and lots of wrong algorithms. I use your test cases and I correct , correct and recorrect my algorithms. They are wrong and wrong on test 4, 2, 5,.. (your test cases). And I got AC on the 2nd submit! Thank you!

6) 01.01 21.59
04.23 11.22
Answer: 5

why it is true?
what is wrong in my&
my program:

var xh1, xh2, yh1, yh2 : real;
    xm1, xm2, ym1, ym2 : real;
    k, km : longint;
begin
read(xh1, yh1, xh2, yh2);
xm1:=trunc(xh1*100) mod 100;
xm2:=trunc(xh2*100) mod 100;
ym1:=trunc(yh1*100) mod 100;
ym2:=trunc(yh2*100) mod 100;
if yh1<xh1 then yh1:=yh1+24;
if yh2<xh2 then yh2:=yh2+24;
xh1:=trunc(xh1);
xh2:=trunc(xh2);
yh1:=trunc(yh1);
yh2:=trunc(yh2);

k:=abs(trunc(0.5*(yh1-yh2+xh2-xh1+trunc( (ym1-ym2+xm2-xm1)/60) )) );

writeln(k);
end.

Thank you a lot.
In your test 6 my program outputs 7.
I forgot that answer should be than 6.
But due to my formula (which,I hope, is correct)the answer
is 7.
Now I have AC.
Thanks!

I couldn't get 1 thing for tests 2 and 6. why answer isn't 7?

if the real time of flight if 17, for 2 test and 14, for 6 test, then 17-7=10 and 14-7=7 (the differences of flights where time is "going back") and 17+7=24 & 14+7=21 (the differences of flights where time is "goting forward").

but if answer is 5 then 10+5=15 24-5=19 (<>) and 7+5=12 and 21-5=16. then wahy this test are true. I know that there must be something that I didn't saw so please help me.
thanks.

I'm don't understand, how can it be:

12.00 15.00
01.02 03.07

It means, that in one way plane fly 3 hours, in other - 2 hours. But in terms said, that times differs not more than 10 minutes.

This test is INCORRECT! Read this post again.