Problem:
Score : 100 points

Problem Statement

There is a right triangle ABC with ∠ABC=90°.

Given the lengths of the three sides, |AB|,|BC| and |CA|, find the area of the right triangle ABC.

It is guaranteed that the area of the triangle ABC is an integer.

Constraints

1 \leq |AB|,|BC|,|CA| \leq 100

All values in input are integers.

The area of the triangle ABC is an integer.

Input

Input is given from Standard Input in the following format:

|AB| |BC| |CA|

Output

Print the area of the triangle ABC.

Sample Input 1

3 4 5

Sample Output 1

6

This triangle has an area of 6.

Sample Input 2

5 12 13

Sample Output 2

30

This triangle has an area of 30.

Sample Input 3

45 28 53

Sample Output 3

630

This triangle has an area of 630.

Solution in Python (3.4.3) (judge verdict: Runtime Error)

from itertools import accumulate
N,K = map(int,input().split())
td = [tuple(map(int,input().split())) for i in range(N)]

td.sort(key=lambda x:-x[1])
td = [(x[0]-1,x[1]) for x in td]
t = [-1]*N
for i in range(N):
    t[td[i][0]] = 0
for i in range(K):
    t[td[:K][i][0]] = 1

t_used = [i for i in range(N) if t[i]==1]
t_not_used = [i for i in range(N) if t[i]==0]

d_top = [0]*N
d_top_candi = [0]*N
d_rest = []
d_candi = []

for i in range(K):
    if t[td[i][0]] == 1:
        if d_top[td[i][0]] == 0:
            d_top[td[i][0]] = td[i][1]
        else:
            d_rest.append(td[i][1])
for i in range(K,N):
    if t[td[i][0]] == 0:
        if d_top_candi[td[i][0]] == 0:
            d_top_candi[td[i][0]] = 1
            d_candi.append(td[i][1])

ans = len(t_used)**2+sum(d_top)
d_rest.sort()
d_candi.sort(key=lambda x:-x)

d_rest_cum = list(accumulate(d_rest))
d_candi_cum = list(accumulate(d_candi))
ans += d_rest_cum[-1]

for k in range(min(len(d_rest),len(d_candi))):
    ans = max(ans + (k+1)*(k+1+2*len(t_used)) + d_candi_cum[k] - d_rest_cum[k],ans)

print(ans)