void Solve(StreamScanner ss, StreamWriter sw)
{
//---------------------------------
N = ss.Next(int.Parse);
C = ss.Next(long.Parse);
XV = ss.Next(long.Parse, 2, N).Select(a => new XVPair(a[0], a[1])).ToArray();
var tr1 = GetMaxValuesOfDist(true, 1);
var tr2 = GetMaxValuesOfDist(true, 2);
var tl1 = GetMaxValuesOfDist(false, 1);
var tl2 = GetMaxValuesOfDist(false, 2);
var max = 0L;
for (var i = 0; i <= N; i++)
{
max = Math.Max(max, tr1[i] + tl2[N - i]);
max = Math.Max(max, tr2[i] + tl1[N - i]);
}
sw.WriteLine(max);
//---------------------------------
}