#include <iostream>
#include <vector>

typedef long long ll;
using namespace std;

ll dp[222222][2];

int main() {
    int N;
    ll P;
    cin >> N >> P;
    vector<ll> H(N);
    for (int i = 0; i < N; i++) {
        cin >> H[i];
    }
    ll INF = 1ll * 100000 * 100000 * 100000 * 1000;
    dp[0][1] = P;
    for (int i = 1; i < N; i++) {
        for (int j = 0; j < 2; j++) {
            int nj = j^1;
            ll diff = (j == 0 ? H[i] - H[i-1] : H[i-1] - H[i]);
            diff = max(0ll, diff);
            ll d1 = dp[i-1][j] + min<ll>(P, diff);
            ll d2 = dp[i-1][nj] + P;
            dp[i][j] = min(d1, d2);
        }
    }
    cout << min(dp[N-1][0], dp[N-1][1]) << endl;
    return 0;
}