#include <iostream>
#include <fstream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <cstring>
#include <string>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <algorithm>
using namespace std;

#define REP(i,n) for(int i=0; i<n; ++i)
#define FOR(i,a,b) for(int i=a; i<=b; ++i)
#define FORR(i,a,b) for (int i=a; i>=b; --i)
#define ALL(c) (c).begin(), (c).end()

typedef long long ll;
typedef vector<int> VI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef vector<VI> VVI;
typedef pair<int,int> P;
typedef pair<ll,ll> PL;

const ll INF = 1e18;

int main() {
    int n;
    ll p;
    cin >> n >> p;
    VL h(n);
    REP(i,n) scanf("%lld", &h[i]);

    VL dpr(n,INF), dpl(n,INF);
    dpr[0] = 0;
    REP(i,n-1){
        dpr[i+1] = min(dpr[i+1], dpr[i] + min(p, max(0LL, h[i+1] - h[i])));
        dpl[i+1] = min(dpl[i+1], dpl[i] + min(p, max(0LL, h[i] - h[i+1])));
        dpr[i+1] = min(dpr[i+1], dpl[i] + p);
        dpl[i+1] = min(dpl[i+1], dpr[i] + p);
    }

    cout << min(dpl[n-1], dpr[n-1]) << endl;

    return 0;
}