N,M=gets.split.map(&:to_i)
h=[]
N.times{
    h<<gets.split.inject(0){|r,i|r+i.to_i}
}
warn h.inspect
r=0
f=true
prev=0
N.times{|i|
    if f
        if (i==0||h[i-1]<h[i])&&(i==N-1||h[i]>h[i+1])
            r+=h[i]
            f=false
        end
    else
        if h[i-1]>h[i]&&i<N-1&&h[i]<h[i+1]
            r-=h[i]
            f=true
        end
    end
}
puts r