intervals = eval(input())
count=intervals[0][0]
minimum = 13829732984
for i in intervals[:-1]:
    if sum(i)<minimum:
        minimum = sum(i)
arr = []
first_min = min(intervals, key = lambda t: t[0])
sum_first_min = sum(first_min)
for i in range(1, minimum+1):
    d=i
    for j in range(0, len(intervals)-1):
        m=count - d*(j+1)
        while m>intervals[j+1][0]+intervals[j+1][1]:
            m-=intervals[j+1][0]+intervals[j+1][1]

        if m<intervals[j+1][0] and m>=0:
            count+=(intervals[j+1][0]-m)
        else:
            if abs(m)>intervals[j+1][1]:
                count+=intervals[j+1][0]-abs(m)
    arr.append(count)
    count=intervals[0][0]

print(max(arr)/len(intervals))