# Here your code !
w,h,n = 3.times.map { gets.to_i }
dp = {}
(1..w).each {|i| dp[i] = {includes: [], excludes: []} }
n.times do
    s,k = gets.split.map(&:to_i)
    (1..w).each do |i|
        if i == s
            dp[i][:excludes] << k
        else
            dp[i][:includes] << k
        end
    end
end

count = dp.inject(0) do |s, (k, v)|
    if v[:excludes].empty?
        s + v[:includes].uniq.size
    else
        s + h - v[:excludes].uniq.size
    end
end

puts count