#include <iostream> #include <utility> #include <vector> #include <string> #include <cmath> #include <algorithm> #include <functional> #include <iomanip> #include <map> #include <set> #include <queue> using namespace std; int main(int argc, char const *argv[]) { int N,D; cin >> N >> D; vector<pair<int,int>> task(N); for(auto &t : task)cin >> t.first >> t.second; vector<vector<int>> dp(N+1,vector<int>(2,-1));// 0 -> Tokyo 1 -> kyoto dp[0][0] = 0; auto chmax = [](int &x, int y) -> int { if(x < y)x = y; return x; }; for(int i=0;i<N;++i) { if(dp[i][0] != -1) { chmax(dp[i+1][0],dp[i][0]+task[i].first); chmax(dp[i+1][1],dp[i][0] + task[i].second - D); } if(dp[i][1] != -1) { chmax(dp[i+1][1],dp[i][1]+task[i].second); chmax(dp[i+1][0],dp[i][1] + task[i].first - D); } } int answer = max(dp[N][0],dp[N][1]); std::cout << answer << std::endl; }