#include <bits/stdc++.h>
#define rep(i, n) for (lli i = 0; i < (n); i++)
#define rrep(i, n) for (lli i = (n)-1; i >= 0; i--)
using namespace std;
using lli = long long int;
int main()
{
    lli n, p;
    cin >> n >> p;
    lli dp[2][200009] = {};
    lli h[200005];
    rep(i, n) cin >> h[i];
    dp[0][0] = 0;
    for (int i = 1; i < n; i++) {
        dp[0][i] = min(min(dp[0][i - 1], dp[1][i - 1]) + p, dp[0][i - 1] + max(h[i] - h[i - 1], 0LL));
        dp[1][i] = min(min(dp[0][i - 1], dp[1][i - 1]) + p, (i != 1 ? dp[1][i - 1] + max(h[i - 1] - h[i], 0LL) : 1000000000000000));
    }
    cout << min(dp[0][n - 1], dp[1][n - 1]) << endl;
    ;
}