import std.stdio, std.conv, std.functional, std.string; import std.algorithm, std.array, std.container, std.range, std.typecons; import std.numeric, std.math, std.random; import core.bitop; string FMT_F = "%.10f"; static string[] s_rd; T RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; } string RDR()() { return readln.chomp; } T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; } size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;} size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; } bool inside(T)(T x, T b, T e) { return x >= b && x < e; } bool minimize(T)(ref T x, T y) { if (x > y) { x = y; return true; } else { return false; } } bool maximize(T)(ref T x, T y) { if (x < y) { x = y; return true; } else { return false; } } long mod = 10^^9 + 7; void moda(ref long x, long y) { x = (x + y) % mod; } void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; } void modm(ref long x, long y) { x = (x * y) % mod; } void main() { auto N = RD; auto M = RD; auto ab = new long[2][](N); auto bests = new long[](N+1); foreach (i; 0..N) { auto A = RD; auto B = RD; ab[i] = [A, B]; if (A > 0) { if (B > A) { bests[i+1] = A * (M-1) + B; } else { bests[i+1] = A * M; } } else if (A * M > B) { bests[i+1] = A * M; } else { bests[i+1] = B; } bests[i+1] += bests[i]; } auto bests2 = new long[](N+1); foreach (i; 0..N) { bests2[i+1] = max(ab[i][0], ab[i][1]); bests2[i+1] += bests2[i]; } auto bests22 = new long[](N+1); bests22[N] = bests2[N]; foreach_reverse (i; 0..N) { bests22[i] = max(bests22[i+1], bests2[i]); } long ans; foreach (i; 0..N) { long x; if (M == 1) x = bests[i+1]; else x = bests[i+1] + bests22[i+1] - bests2[i+1]; ans = max(ans, x); } debug writeln(bests); debug writeln(bests2); writeln(ans); stdout.flush(); debug readln(); }