open System

let ri () = stdin.ReadLine() |> int
let ria () = stdin.ReadLine().Split() |> Array.map int

type Sol() =
    member this.Solve() = 
        let W = stdin.ReadLine() |> int64
        let H = stdin.ReadLine() |> int64
        let N = stdin.ReadLine() |> int
        let mutable (L : list<int*int> ) = []
        
        for i in 1..(int N) do
            let (s,k) = (ria () ) |> (fun ar -> (ar.[0], ar.[1]) )
            L <- (s,k) :: L
        
        let hu = L |> List.map fst |> List.distinct |> List.length |> int64
        let wu = L |> List.map snd |> List.distinct |> List.length |> int64
        
        W*H - (W-wu)*(H-hu) - (int64 N) |> printfn "%d"
        
        
let mySol = new Sol()
mySol.Solve()