main :: IO()
main = getContents >>= putStrLn . show . listToValue . (map readDouble) . words


readDouble :: [Char] -> Int
readDouble = read

hours :: Int -> Int
hours x = x * 3600

minutes :: Int -> Int
minutes x = x * 60

listToValue :: [Int] -> Int
listToValue (x:y:z:_)
  | minutes x == y = -1
  | result < 0 = -1
  | otherwise = result
  where
    -- calc :: (RealFrac a , Integral b) => a -> a -> a -> b
    calc :: Int -> Int -> Int -> Int
    calc x y z = ceiling ( ( (toDouble (hours z)) / (toDouble ((minutes x) - y))))
    result = calc x y z

toDouble:: Int -> Double
toDouble x = fromIntegral x