import math n = int(input().strip().split(" ")[0]) data = [] datastr = input().strip() diff = math.inf res = 0 for i in datastr.split(","): cur1, cur2 = map(int, i.split(":")) data.append([cur1, cur2]) if abs(cur1 - n) < diff: diff = abs(cur1 - n) res = cur2 elif abs(cur1 - n) == diff: res = (res + cur2) / 2.0 print("%.1f" % res)