import std.conv, std.functional, std.range, std.stdio, std.string; import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons; import core.bitop; class EOFException : Throwable { this() { super("EOF"); } } string[] tokens; string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; } int readInt() { return readToken.to!int; } long readLong() { return readToken.to!long; } string COLOR(string s = "") { return "\x1b[" ~ s ~ "m"; } bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } } bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } } int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; } int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); } int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); } void main() { try { for (; ; ) { const N = readInt; const M = readLong; auto A = new long[N + 2]; foreach (i; 1 .. N + 1) A[i] = readLong; auto B = new long[N + 2]; foreach (i; 1 .. N + 1) B[i] = readLong; auto C = new long[N + 2]; foreach (i; 1 .. N + 1) { C[i] = (A[i] - B[i]) % M; if (C[i] < 0) C[i] += M; } auto D = new long[N + 1]; foreach (i; 0 .. N + 1) { D[i] = C[i + 1] - C[i]; if (D[i] < 0) D[i] += M; } const sumD = D.sum; debug { writeln("D = ", D); writeln("sumD = ", sumD); } auto costs = new long[N + 1]; foreach (i; 0 .. N + 1) { costs[i] = (M - D[i]) - D[i]; } costs.sort; long ans; ans += sumD; ans += costs[0 .. sumD / M].sum; ans /= 2; writeln(ans); } } catch (EOFException e) { } }