https://icpcarchive.ecs.baylor.edu/external/37/3774.pdf

problem3774.py

f=open("3774.txt","r")
try:
    while True:
        b=[tuple(f.readline().strip().split(",")+[0]) for i in range(int(f.readline().strip()))]
        a=reduce(lambda a,b:(b[0],b[1],a[2]+((float(b[0])-float(a[0]))*((float(a[1])+float(b[1]))/2))),b)
        print "%.2f to %.2f: %.4f" % (float(b[0][0]),float(a[0]),a[2])
except:
    pass