#include using namespace std; using pii = pair; using ll = long long; #define rep(i, j) for(int i=0; i < (int)(j); i++) #define repeat(i, j, k) for(int i = (j); i < (int)(k); i++) #define all(v) v.begin(),v.end() #define debug(x) cerr << #x << " : " << x << endl template bool set_min(T &a, const T &b) { return a > b ? a = b, true : false; } template bool set_max(T &a, const T &b) { return a < b ? a = b, true : false; } // vector template istream& operator >> (istream &is , vector &v) { for(T &a : v) is >> a; return is; } template ostream& operator << (ostream &os , const vector &v) { for(const T &t : v) os << "\t" << t; return os << endl; } // pair template ostream& operator << (ostream &os , const pair &v) { return os << "<" << v.first << ", " << v.second << ">"; } const int INF = 1 << 30; const ll INFL = 1LL << 60; class Solver { public: bool solve() { ll N, P; cin >> N >> P; vector H(N); cin >> H; int i = 0; auto gezan = [&] () { while(i + 1 < N and H[i] >= H[i + 1]) i++; }; auto tozan = [&] () { ll sum = 0; while(i + 1 < N and H[i] <= H[i + 1]) { sum += H[i + 1] - H[i]; i++; } return sum; }; ll ans = 0; while(i + 1 < N) { gezan(); ll cost = tozan(); ans += min(P * (i + 1 < N ? 2 : 1), cost); } cout << ans << endl; return 0; } }; int main() { cin.tie(0); ios::sync_with_stdio(false); Solver s; s.solve(); return 0; }