A=[0]*3
for i in range(3):
  A[i]=int(input())
#print(A)
ans=int((A[0]+A[1])*A[2]/2)
print(ans)
6500cc8bcb8389afdb7778ac33984ac389208d1e
<mask token>

<mask token>
for i in range(3):
    A[i] = int(input())
<mask token>
print(ans)

A = [0] * 3
for i in range(3):
    A[i] = int(input())
ans = int((A[0] + A[1]) * A[2] / 2)
print(ans)

A=[0]*3
for i in range(3):
  A[i]=int(input())
#print(A)
ans=int((A[0]+A[1])*A[2]/2)
print(ans)