858 B | 858 chars
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from decimal import Decimal
BLANK = " "
#inp = input
inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
while 1:
l = []
a, b = mfi()
if a == b == -1:
break
l.append([a, b])
while 1:
a, b = mfi()
if a == b == 0:
break
l.append([a, b])
dis = 0
fuel = 0
for i in range(len(l) - 1):
fir = l[i]
sec = l[i+1]
if fir[1] < sec[1]:
continue
dis += sec[0] - fir[0]
fuel += fir[1] - sec[1]
p(round(l[-1][1] * dis / fuel))
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()