You are given the array `paths`, where `paths[i] = [cityAi, cityBi]` means there exists a direct path going from `cityAi` to `cityBi`. Return the destination city, that is, the city without any path outgoing to another city.

It is guaranteed that the graph of paths forms a line without any loop, therefore, there will be exactly one destination city.

Example 1:

    Input: paths = [["London","New York"],["New York","Lima"],["Lima","Sao Paulo"]]
    Output: "Sao Paulo"
    Explanation: Starting at "London" city you will reach "Sao Paulo" city which is the destination city. Your trip consist of: "London" -> "New York" -> "Lima" -> "Sao Paulo".

Example 2:

    Input: paths = [["B","C"],["D","B"],["C","A"]]
    Output: "A"
    Explanation: All possible trips are:
    "D" -> "B" -> "C" -> "A".
    "B" -> "C" -> "A".
    "C" -> "A".
    "A".
    Clearly the destination city is "A".

Example 3:

    Input: paths = [["A","Z"]]
    Output: "Z"

Constraints:

- `1 <= paths.length <= 100`
- `paths[i].length == 2`
- `1 <= cityAi.length, cityBi.length <= 10`
- `cityAi != cityBi`
- All strings consist of lowercase and uppercase English letters and the space character.