func input() -> (Int, Int)? {
    let input = readLine()
    if let text = input {
        let numbers = text.split(separator: " ")
        if numbers.count == 2 {
            if let number1 = Int(numbers[0]), let number2 = Int(numbers[1]) {
                return (number1, number2)
            }
        }
    }
    return nil
}

func checkPairs() -> String {
    guard let (lectures, pairs) = input() else { return "NO" }
    guard lectures < 10000 && lectures >= 1 else { return "NO"}
    guard pairs < 10000 && pairs >= 0 else { return "NO"}
    for _ in 0..<pairs {
        guard let (lecture2, lecture1) = input() else { return "NO" }
        guard lecture1 < lectures && lecture1 >= 0 else { return "NO"}
        guard lecture2 < lectures && lecture2 >= 0 else { return "NO"}
        if lecture2 <= lecture1 {
            return "NO"
        }
    }
    return "YES"
}

print(checkPairs())