import sys
from math import sqrt, pi, sin
inp = lambda : sys.stdin.readline()[:-1]
mii = lambda x = " ": [*map(int,input().split(x))]
mfi = lambda x = " ": [*map(float,input().split(x))]
ii = lambda : int(input())
ans = 0
for i in range(ii()):
d, w = mii()
th = d * pi / 180
ans += sin(th) * w
print("{:.2f}".format(ans))