var ans: Int = 0
var cur: Int = 0

for _ in 0...9 {
    guard let info = readLine() else { break }

    let io = info.split(separator : " ").compactMap{Int($0)}
    guard io.count == 2 else { break }

    cur += io[1] - io[0]
    ans = max(ans, cur)
}

print(ans)