Problem:
 Score : 100 points    Problem Statement You are given a trapezoid. The lengths of its upper base, lower base, and height are a , b , and h , respectively.    An example of a trapezoid   Find the area of this trapezoid.      Constraints  1≦a≦100  1≦b≦100  1≦h≦100  All input values are integers.  h is even.         Input The input is given from Standard Input in the following format:  a  b  h       Output Print the area of the given trapezoid. It is guaranteed that the area is an integer.        Sample Input 1 3
4
2      Sample Output 1 7  When the lengths of the upper base, lower base, and height are 3 , 4 , and 2 , respectively, the area of the trapezoid is (3+4)×2/2 = 7 .       Sample Input 2 4
4
4      Sample Output 2 16  In this case, a parallelogram is given, which is also a trapezoid.

Solution (Python):
a, b, h = int(input()), int(input()), int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h*0.5))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a,b,h = [int(input()) for _ in range(3)]
print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a+b)*h//2)

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

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
S = (a+b)*h
print(S//2)

Solution (Python):

	
def main():	
	x = int(input())
	y = int(input())
	h = int(input())
	print(((x + y) * h) // 2)
 
if __name__ == "__main__":
	main()

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a,b,h=map(int,open(0));print((a+b)*h//2)

Solution (Python):
print((int(input())+int(input()))*int(input())//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

ans = ((a+b)*h)*0.5

print(int(ans))

Solution (Python):
a,b,h=map(int,open(0));print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a+b)*h//2)

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

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a + b) * h / 2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a + b) * h // 2))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):

a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(h*b - (b-a)*h*1//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h*0.5))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
c = int(input())
print(int(((a+b)*c)/2))

Solution (Python):
print((int(input()) + int(input())) * int(input()) // 2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h /2))

Solution (Python):
N = []
for i in range(3):
    N.append(input())
N = list(map(int, N))
a, b, h = N[0], N[1], N[2]
s = (a + b) * h / 2
print(int(s))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a + b) * (h / 2)))

Solution (Python):
print((int(input())+int(input()))*int(input())//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
 
print(int((a + b) * h / 2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

s = (a + b) * h / 2
  
print(int(s))

Solution (Python):
import sys
import copy
import math
import string
from _bisect import *
from collections import *
from operator import itemgetter
from math import factorial

from fractions import gcd
def lcm(x, y):
    return (x * y) // gcd(x, y)


stdin = sys.stdin
ni = lambda: int(ns())
na = lambda: list(map(int, stdin.readline().split()))
ns = lambda: stdin.readline()

a = ni()
b = ni()
h = ni()
print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a+b)*h//2)

Solution (Python):
a = int(input())
b= int(input())
h=int(input())

print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a + b) * h // 2)

Solution (Python):
def main():
    a = int(input())
    b = int(input())
    h = int(input())
    print(int((a + b) * h / 2))
if __name__ == '__main__':
    main()

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
x=[]
for i in range(3):
  x.append(int(input()))
print(int((x[0]+x[1])*x[2]/2))

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

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print(int((a+b)*h//2))

Solution (Python):
a,b,h = [int(input()) for i in range(3)]
print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())

print(int((a+b)*h/2))

Solution (Python):
a,b,h=map(int,open(0).read().split())
print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
s=(a+b)*h/2
s=int(s)
print(s)

Solution (Python):
a, b, h = (int(input()) for i in range(3))
print(int((a+b)/2*h))

Solution (Python):
def main():

    a = int(input())
    b = int(input())
    h = int(input())

    return (a+b)*h//2

if __name__ == '__main__':
    print(main())

Solution (Python):
a, b, h = [int(input()) for _ in range(3)]
print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
A = int(input())
B = int(input())
H = int(input())
print(int((A+B)*H/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h*1//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a, b, h = [int(input()) for _ in range(3)]
print((a + b) * h // 2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())//2
print((a+b)*h)

Solution (Python):
a,b,h=map(int,open(0));print((a+b)*h//2)

Solution (Python):
a,b,h=map(int,open(0));print((a+b)*h//2)

Solution (Python):
a,b,h=eval('int(input()),'*3);print((a+b)*h//2)

Solution (Python):
print((int(input()) + int(input())) * int(input()) // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a + b) *h /2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int(1/2*(a+b)*h))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(((a+b)*h)//2)

Solution (Python):

a = int(input()) 
b = int(input()) 
h = int(input())

s = (a + b) * h/2
print(round(s))

Solution (Python):
class AtCoder:
    def main(self):
        a, b, h = [int(input()) for _ in range(3)]
        return (a + b) * h // 2


if __name__ == '__main__':
    print(AtCoder().main())

Solution (Python):
print(int(((int(input())+int(input()))*int(input()))/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

answer = (a + b) * h /2

print(int(answer))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a,b,h = [int(input()) for i in range(3)]
print(h*(a+b)//2)

Solution (Python):
a, b, h = [int(input()) for _ in range(3)]
print((a + b)*h // 2)

Solution (Python):
a,b,c=map(int,open(0).read().split())
print((a+b)*c//2)

Solution (Python):
a, b, h = [int(input()) for i in range(3)]
s = int((a+b)*h/2)
print(s)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*(h/2)))

Solution (Python):
a, b, h = map(int, [input() for i in range(3)])
print(int((a + b) * h / 2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
S = (a+b)*h/2
print(int(S))

Solution (Python):
print(int((int(input())+int(input()))*int(input())/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())

print((a+b)*h//2)

Solution (Python):
a=int(input());b=int(input());h=int(input());print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print ((a+b)*h //2)

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

Solution (Python):
a = int(input())
b = int(input())
c = int(input())

print((a+b) * c //2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a + b) * h / 2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a+b)*h//2)

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

Solution (Python):
print((int(input()) + int(input())) * int(input()) // 2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())

print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a=[int(input()) for i in range(3)];print((a[0]+a[1])*a[2]//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

ans = (a + b) * h / 2
ans = int(ans)

print(ans)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
print((int(input())+int(input()))*int(input())//2)

Solution (Python):
a, b, h = [int(input()) for i in range (3)]

print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
r = (a+b)*h//2
print(r)

Solution (Python):
str = [int(input()) for i in range(3)]

area = (str[0]+str[1])*str[2]/2

print(round(area))

Solution (Python):
import sys
import bisect
input = sys.stdin.readline
 
def main():
    a=int(input())
    b=int(input())
    h=int(input())
    
    ans=int((a+b)*h/2)
    
    print(ans)
    
main()

Solution (Python):
x = lambda:int(input())
print((x()+x())*x()//2)

Solution (Python):
a,b,h= map(int,open(0).read().split())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

ans = (a + b) * h / 2
print(round(ans))

Solution (Python):

a = int(input())
b = int(input())
h = int(input())

print ( (a+b)*h // 2 )

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
S = ((a+b)*h)/2
print(int(S))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

S = ((a+b)*h)/2
print(int(S))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print(int((a+b)*h*0.5))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a*h//2)+(b*h//2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

ans = (a + b) * h / 2
print(int(ans))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):

a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):

a = int(input())
b = int(input())
h = int(input())

S = (a + b) * h / 2
print(int(S))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h/2))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())

print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h/2))

Solution (Python):
a = float(input())
b = float(input())
h = float(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a + b) * h / 2))

Solution (Python):
a,b,h=int(input()),int(input()),int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a = int( input() )
b = int( input() )
h = int( input() )

print( int( (a+b)*h*0.5 ) )

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int( (a + b) * h / 2))

Solution (Python):
a, b, h = [int(input()) for i in range(3)]
print(int((a+b)*h/2))

Solution (Python):
a, b, h = [int(input()) for _ in range(3)]
print(int((a+b)*h/2))

Solution (Python):
a, b, h = [int(input()) for _ in range(3)]
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
c = int(input())
print(int((a+b)*c/2))

Solution (Python):
import sys
input = sys.stdin.readline

a = int(input())
b = int(input())
h = int(input())
ans = (a+b) * h * 0.5
print(int(ans))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
d=a+b
print(int(d*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print("%d" % ((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(((a+b)*h)//2)

Solution (Python):
ue = int(input())
shita = int(input())
h = int(input())
print(int((ue+shita)*h/2))

Solution (Python):
a, b, h = [int(input()) for _ in range(3)]
print((a+b)*h//2)

Solution (Python):
a,b,h = [int(input()) for _ in range(3)]
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
H = int(input())

print((a+b)*(H//2))

Solution (Python):
a, b, h = [int(input()) for i in range(3)]

print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h*0.5))

Solution (Python):
a, b, h = map(int,open(0).read().split())
print(round(((a+b)* h / 2)))

Solution (Python):
a, b, c = map(int, open(0))
print((a + b) * (c // 2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h/2))

Solution (Python):
a, b, h = [int(input()) for i in range(3)]
size = (a + b) * h / 2
print(int(size))

Solution (Python):
a,b,h=[int(input()) for i in range(3)]

s=(a+b)*h/2
s=int(s)

print(s)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a + b) * h / 2))

Solution (Python):
a,b,h = int(input()),int(input()),int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

ans = (a+b)*h//2
print(ans)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

ans = (a+b)*h/2

print(int(ans))

Solution (Python):
a,b,h= [int(input()) for i in range(3)]
print(int((a+b)*h/2))

Solution (Python):

import sys

def main():
    a = int(input())
    b = int(input())
    h = int(input())
    print((a + b) * h // 2)


if __name__ == '__main__':
    main()

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a+b)*h//2)

Solution (Python):

import sys
sys.setrecursionlimit(300000)


def solve(a: int, b: int, h: int):
    ret = (b + a) * h / 2
    print(int(ret))
    return


def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    a = int(next(tokens))  
    b = int(next(tokens))  
    h = int(next(tokens))  
    solve(a, b, h)

if __name__ == '__main__':
    main()

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
print((int(input()) + int(input())) * int(input()) // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
print((int(input())+int(input()))*int(input())//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
s = int((a+b)*h/2)
print(s)

Solution (Python):
a = int(input())
b = int(input())
c = int(input())

print((a + b) * c // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(((a + b) * h) // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
 
print(h * (a+b) // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
c = int(input())
print(round((a+b)*c/2))

Solution (Python):
a,b,h = [int(input()) for i in range(3)]
print(h*(a+b)//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print(int(((a+b)*h)/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
ans = (a + b) * h // 2
print(ans)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
import sys, re, os
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
from itertools import permutations, combinations, product, accumulate
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from fractions import gcd
 
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def S_MAP(): return map(str, input().split())
def LIST(): return list(map(int, input().split()))
def S_LIST(): return list(map(str, input().split()))

sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

a = INT()
b = INT()
h = INT()
ans = (a + b) * h /2
print(int(ans))

Solution (Python):
A = int(input())
B = int(input())
H = int(input())
print((A+B)*H//2)

Solution (Python):
a = int(input())
b = int(input())
c = int(input())

print((a+b) * round(c/2))

Solution (Python):

a = int(input())
b = int(input())
h = int(input())

print(int((a + b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

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

Solution (Python):
a = int(input())
b = int(input())
c = int(input())
print((a+b)*c//2)

Solution (Python):

a = int(input())
b = int(input())
h = int(input())

print  (((a+b)*h) // 2 )

Solution (Python):

from collections import defaultdict
from collections import deque
from heapq import heappush, heappop
import sys
import math
import bisect
import random
import itertools
sys.setrecursionlimit(10**5)
stdin = sys.stdin
bisect_left = bisect.bisect_left
bisect_right = bisect.bisect_right
def LI(): return list(map(int, stdin.readline().split()))
def LF(): return list(map(float, stdin.readline().split()))
def LI_(): return list(map(lambda x: int(x)-1, stdin.readline().split()))
def II(): return int(stdin.readline())
def IF(): return float(stdin.readline())
def LS(): return list(map(list, stdin.readline().split()))
def S(): return list(stdin.readline().rstrip())
def IR(n): return [II() for _ in range(n)]
def LIR(n): return [LI() for _ in range(n)]
def FR(n): return [IF() for _ in range(n)]
def LFR(n): return [LI() for _ in range(n)]
def LIR_(n): return [LI_() for _ in range(n)]
def SR(n): return [S() for _ in range(n)]
def LSR(n): return [LS() for _ in range(n)]
mod = 1000000007
inf = float('INF')


def A():
    a, b, h = IR(3)
    print((a+b)*h//2)
    return


def B():
    return


def C():
    return


def D():
    return


def E():
    return


def F():
    return


def G():
    return


def H():
    return


if __name__ == '__main__':
    A()

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a,b,h=map(int,open(0))
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
print(int((int(input())+int(input()))*int(input())/2))

Solution (Python):
print(int((int(input())+int(input()))*int(input())/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a + b) * h / 2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a + b) * h // 2)

Solution (Python):
a, b, h = (int(input()) for i in range(3))
print(int((a + b) * h / 2))

Solution (Python):
a = int(input())
b = int(input())
c = int(input())
print((a + b) * c // 2)

Solution (Python):



a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h/2))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a, b, h = [int(input()) for i in range(3)]
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h*(1/2)))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h*0.5))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a + b) * h // 2)

Solution (Python):


def solve():
    a = int(input())
    b = int(input())
    h = int(input())
    print(int((a+b)*h//2))

if __name__ == "__main__":
    solve()

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

ans = (a + b) * h // 2
print(ans)

Solution (Python):
a,b,h = [int(input()) for _ in range(3)]
print(int((a+b)*h*(1/2)))

Solution (Python):
def main():
    a = int(input())
    b = int(input())
    h = int(input())
    print(int((a+b)*h/2))

if __name__ == '__main__':
    main()

Solution (Python):
a = int(input())
b = int(input())
c = int(input())

d = (a+b)*c/2

print(int(d))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print( (a+b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
c = int(input())
print(int(c*(a+b)*0.5))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
area = (a+b)*h/2
print(int(area))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a + b) * h / 2))

Solution (Python):
a=input()
b=input()
h=input()
a=int(a)
b=int(b)
h=int(h)
x=(a+b)*h
print(x//2)

Solution (Python):
a= int(input())
b= int(input())
h= int(input())
print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print(int((a+b)/2*h))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h/2))

Solution (Python):
a,b,h = [int(input()) for i in range(3)]
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a + b) * h / 2))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
print((int(input()) + int(input())) * int(input()) // 2)

Solution (Python):
l = []
for i in range(3):
	l.append(int(input()))
print(int((l[0] + l[1]) * l[2]/2))

Solution (Python):
a = int(input()) 
b = int(input())
h = int(input())

print(int(1/2*(a+b)*h))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
nl = lambda: list(map(int, input().split()))
sl = lambda: input().split()
n = lambda: int(input())
s = lambda: input()

a = n()
b = n()
h = n()

print((a +b )*h // 2)

Solution (Python):
a=int(input())
b=int(input())
c=int(input())
print(((a+b)*c)//2)

Solution (Python):
import math
a =int(input())
b =int(input())
h =int(input())
print((a+b)*h//2)

Solution (Python):
import math
a =int(input())
b =int(input())
h =int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a, b, h = int(input()), int(input()), int(input())
print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a + b) * h // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a+b)*h//2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print(int((a+b)*h/2))

Solution (Python):


a = int(input())
b = int(input())
c = int(input())

daikei = (a + b) * c / 2

print(int(daikei))

Solution (Python):
x = int(input())
y = int(input())
z = int(input())

print((x + y) * z //2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
ans = (a+b) * h // 2
print(ans)

Solution (Python):
a, b, h = [int(input()) for _ in range(3)]
print(h * (a + b) // 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):

import copy
import random
import bisect 
import fractions 
import math
import sys

mod = 10**9+7
sys.setrecursionlimit(mod) 


a = int(input())
b = int(input())
h = int(input())

print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a + b) * h / 2))

Solution (Python):
def abc():
    a = int(input())
    b = int(input())
    h = int(input())
    print(int((a + b) * h / 2))


abc()

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

ans = int((a+b)*h/2)

print(ans)

Solution (Python):
a,b,h=[int(input()) for i in range(3)]
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):


a, b, h = int(input()),int(input()),int(input())

print(int((a+b)*h/2))

Solution (Python):
s = [int(input()) for i in range(3)]
print(int((s[0] + s[1]) * s[2] * 0.5))

Solution (Python):
s = input()
x = input()
b = input()
a = s + x
c = b / 2
print a * c

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print(int((a+b)*h/2))

Solution (Python):
N = int(input())
K = int(input())
X = int(input())
print((N+K)*X//2)

Solution (Python):
A = int(input()) 
B = int(input()) 
C = int(input())
print((A+B)*C//2)

Solution (Python):
a,b,h=[int(input()) for i in range(1,4)]
s=int((a+b)*h/2)
print(s)

Solution (Python):
a, b, h = [int(input()) for _ in range(3)]

print((a+b) * h // 2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

size = int((a+b) * h / 2)

print(size)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
ans = (a+b)*h/2
print(int(ans))

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print(int((a+b)*h/2))

Solution (Python):
a=[int(input()) for _ in range(3)]
print((a[0]+a[1])*a[2]//2)

Solution (Python):
a,b,h=map(int,open(0));print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
c = int(input())

print((a+b)*c//2)

Solution (Python):
a=int(input())
b=int(input())
c=int(input())
print(((a+b)*c)//2)

Solution (Python):

a = int(input())
b = int(input())
h = int(input())
print(int((a+b)*h/2))

Solution (Python):
a = int(input())
b = int(input())
c = int(input())
print(int(((a+b)*c/2)))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

result = h * (a + b) / 2
result = int(result)

print(result)

Solution (Python):
n = [int(input()) for _ in [0]*3]
print( int(((n[0]+n[1])*n[2])/2) )

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
square = (a + b) * h / 2
print(int(square))

Solution (Python):
l=[]
for i in range(3):
   l.append(int(input())) 
print(int((l[0]+l[1])*l[2]/2))

Solution (Python):
a = int(input()); b = int(input()); h = int(input())
print((a+b)*h//2)

Solution (Python):

import sys
def input(): return sys.stdin.readline().rstrip()
def mi(): return map(int, input().split())


a = int(input())
b = int(input())
h = int(input())

print(round((a+b)*h/2))

Solution (Python):
a = []
for i in range(3):
   a.append(input())
print((a[0] + a[1]) * a[2] / 2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):




def main():
	a = int(input())
	b = int(input())
	h = int(input())
	ans = (a+b)*h
	print(int(ans/2))


if __name__ == '__main__':
	import sys
	sys.exit(main())

Solution (Python):
a=int(input())
b=int(input())
z=int(input())
print(int((a+b)*z/2))

Solution (Python):
print((int(input())+int(input()))*int(input())//2)

Solution (Python):
import sys, os

f = lambda:list(map(int,input().split()))
if 'local' in os.environ :
    sys.stdin = open('./input.txt', 'r')



def solve():
    a = f()[0]
    b = f()[0]
    h = f()[0]
    print((a+b)*h//2)

solve()

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*(int(h/2)))

Solution (Python):
X = []
for i in range(3):
  X.append(int(input()))
print(int((X[0] + X[1])*X[2]/2))

Solution (Python):
[a, b, h] = [int(input()) for i in range(3)]
print(int((a + b) * h / 2))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a + b) * h // 2)

Solution (Python):
a, b, c = [int(input()) for _ in range(3)]
print((a + b) * c // 2)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

ans = (a+b) * h / 2
print(int(ans))

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
l = [int(input()) for i in range(3)]
s = int((l[0] + l[1]) * l[2] / 2)
print(s)

Solution (Python):
a=int(input())
b=int(input())
h=int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
ans = int((a+b)*h/2)
print(ans)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())
print((a+b)*h//2)

Solution (Python):
a = int(input())
b = int(input())
h = int(input())

print((a + b) * h // 2)