9638. Easy problem for Dino
Given two
different integers a and b. Find such integer k that |a – k| = |b – k|.
Note: |x| means the absolute value of x.
Input. Two integers a and b (-109 ≤ a, b ≤ 109, a ≠ b).
Output. If the value of k doesn’t exist, print “-”. Otherwise
print k.
|
Sample
input 1 |
Sample
output 1 |
|
10 5 |
- |
|
|
|
|
Sample
input 2 |
Sample
output 2 |
|
6 2 |
4 |
mathematics
The equation |a – k| = |b – k| is equivalent to
one of the following:
·
a – k
= b – k or a = b, which
is impossible because a ≠ b;
·
a – k
= k – b or 2k
= a + b, k = (a
+ b) / 2;
The solution
exists if a + b is divisible by
2.
Example
In the second
test we have the equation: |6 – k|
= |2 – k|, wherefrom
6 – k
= k – 2, 2k = 8, k = 4
Algorithm realization
Read the
input data.
scanf("%lld %lld",
&a, &b);
If a + b is not divisible by 2, then there is no
solution. Otherwise the answer is (a + b)
/ 2.
c = a + b;
if (c % 2 != 0) printf("-\n");
else printf("%lld\n", c /
2);