#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; using ll = long long; const ll MAX_V = 1010; const ll MAX_E = 2010; ll V, E; struct edge { ll from, to, cost; }; edge ES[MAX_E]; ll d[MAX_V]; const char alphabet[26] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'}; const ll MOD = (ll) 1e9 + 7; const int MAX_INT = 1 << 17; #define all(x) (x).begin(),(x).end() #define PRI(n) cout << n < C(r + 1); C[0] = 1; FOR(i, 1, n) for (int j = min(i, r); j < 1; --j)C[j] = (C[j] + C[j - 1]) % MOD; return C[r]; } template class SegTree { int n; vector data; T def; function operation; function update; T _query(int a, int b, int k, int l, int r) { if (r <= a || b <= l) return def; if (a <= l && r <= b) return data[k]; else { T c1 = _query(a, b, 2 * k + 1, l, (l + r) / 2); T c2 = _query(a, b, 2 * k + 2, (l + r) / 2, r); return operation(c1, c2); } } public: SegTree(size_t _n, T _def, function _operation, function _update) : def(_def), operation(_operation), update(_update) { n = 1; while (n < _n) { n *= 2; } data = vector(2 * n - 1, def); } void change(int i, T x) { i += n - 1; data[i] = update(data[i], x); while (i > 0) { i = (i - 1) / 2; data[i] = operation(data[i * 2 + 1], data[i * 2 + 2]); } } T query(int a, int b) { return _query(a, b, 0, 0, n); } T operator[](int i) { return data[i + n - 1]; } }; struct UnionFind { vector par; vector rank; UnionFind(int N) { for (int i = 0; i < N; ++i) { par.push_back(i); rank.push_back(0); } } int find(int x) { if (par[x] == x)return x; else return par[x] = find(par[x]); } void unite(int x, int y) { x = find(x); y = find(y); if (x == y)return; if (rank[x] < rank[y])par[x] = y; else { par[y] = x; if (rank[x] == rank[y])rank[x]++; } } bool same(int x, int y) { return find(x) == find(y); } }; struct ListNode { int val; ListNode *next; ListNode(int x) : val(x), next(NULL) {} }; void Bellman_short(int s) { REP(i, V)d[i] = 1LL << 50; d[s] = 0; REP(i, V) REP(i, E) { edge e = ES[i]; if (d[e.from] != 1LL << 50 && d[e.to] > d[e.from] + e.cost) { d[e.to] = d[e.from] + e.cost; } } } bool Bellman_negLoop(int s) { REP(i, V)d[i] = 1LL << 50; d[s] = 0; REP(i, V) REP(j, E) { edge e = ES[j]; if (d[e.from] != 1LL << 50 && d[e.to] > d[e.from] + e.cost) { d[e.to] = d[e.from] + e.cost; if (i == V - 1)return true; } } return false; } int main() { int N, M; cin >> N >> M; vector A(N), B(N); REP(i, N)cin >> A[i] >> B[i]; int dp[1000][2]; dp[0][0] = A[0], dp[0][1] = B[0] - M; FOR(i, 1, N-1) { dp[i][0] = A[i] + max(dp[i - 1][0], dp[i - 1][1] - M); dp[i][1] = B[i] + max(dp[i - 1][0] - M, dp[i - 1][1]); } PRI(max(dp[N - 1][0], dp[N - 1][1])) return 0; }