#include <bits/stdc++.h> using namespace std; typedef pair<int, int> pii; typedef double ll; int _N, _L; vector<pii> u2d, d2u; vector<ll> dpmu, dpmd; ll dpu(int index); ll dpd(int index); int main(void) { scanf("%d%d", &_N, &_L); int i; for (i = 0; i < _N; i++) { int a, b; scanf("%d%d", &a, &b); u2d.push_back(pii(a, b)); d2u.push_back(pii(b, a)); } sort(u2d.begin(), u2d.end()); sort(d2u.begin(), d2u.end()); dpmu.assign(_N, 0); dpmd.assign(_N, 0); ll mx = 0; for (i = 0; i < _N; i++) mx = max(mx, dpu(i)); for (i = 0; i < _N; i++) mx = max(mx, dpd(i)); printf("%lld", (long long)mx); return 0; } ll dpu(int index) { if (dpmu[index] != 0) return dpmu[index]; ll ret = u2d[index].first - u2d[index].second; ret = abs(ret) + _L; ll mn = ret; int fr = lower_bound(d2u.begin(), d2u.end(), pii(u2d[index].second, 0)) - d2u.begin(); int to = lower_bound(d2u.begin(), d2u.end(), pii(u2d[index].second, u2d[index].first)) - d2u.begin(); for (int i = fr; i < to; i++) ret = max(ret, mn + dpd(i)); return dpmu[index] = ret; } ll dpd(int index) { if (dpmd[index] != 0) return dpmd[index]; ll ret = d2u[index].first - d2u[index].second; ret = abs(ret) + _L; ll mn = ret; int fr = lower_bound(u2d.begin(), u2d.end(), pii(d2u[index].second, 0)) - u2d.begin(); int to = lower_bound(u2d.begin(), u2d.end(), pii(d2u[index].second, d2u[index].first)) - u2d.begin(); for (int i = fr; i < to; i++) ret = max(ret, mn + dpu(i)); return dpmd[index] = ret; }

game.cpp: In function 'int main()':
game.cpp:17:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d", &_N, &_L);
     ~~~~~^~~~~~~~~~~~~~~~~~
game.cpp:23:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d", &a, &b);
         ~~~~~^~~~~~~~~~~~~~~~