#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) REP(i,0,n)
#define REP(i,s,e) for(int i=(s); i<(int)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for(int i=(int)(s-1); i>=(int)(e); i--)
#define all(r) r.begin(),r.end()
#define rall(r) r.rbegin(),r.rend()

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;

const ll INF = 1e18;
const ll MOD = 1e9 + 7;

template<typename T> T chmax(T& a, const T& b){return a = (a > b ? a : b);}
template<typename T> T chmin(T& a, const T& b){return a = (a < b ? a : b);}
#define DEBUG_MODE
#ifdef DEBUG_MODE
#define dump(x) cout << #x << " : " << x << " "
#define dumpL(x) cout << #x << " : " << x << '\n'
#define LINE cout << "line : " << __LINE__ << " "
#define LINEL cout << "line : " << __LINE__ << '\n'
#define dumpV(v) cout << #v << " : ["; for(auto& t : v) cout << t << ", "; cout<<"]" << " "
#define dumpVL(v) cout << #v << " : ["; for(auto& t : v) cout << t << ", "; cout<<"]" << endl
#define STOP assert(false)
#else
#define dump(x) 
#define dumpL(x) 
#define LINE 
#define LINEL 
#define dumpV(v) 
#define dumpVL(v) 
#define STOP assert(false)
#endif
#define mp make_pair
 
namespace std {
template<class S, class T>
ostream &operator <<(ostream& out, const pair<S, T>& a) {
    out << '(' << a.fi << ", " << a.se << ')';
    return out;
}
}

int main(){
    ll n, p;
    cin >> n >> p;
    vl h(n);
    rep(i, n) cin >> h[i];
    vl left(n);
    iota(all(left), 0);
    REP(i, 1, n) if(h[i-1] <= h[i]) left[i] = left[i-1];
    vector<vl> dp(n, vl(2,INF));
    dp[0][0] = 0LL;
    REP(i, 1, n) {
        chmin(dp[i][0], dp[i-1][0]+min(p, max(0LL, h[i]- h[i-1])));
        chmin(dp[i][0], dp[i-1][1]+p);
        chmin(dp[i][1], dp[i-1][1]+min(p, max(0LL, h[i-1]- h[i])));
        {
            int j = left[i]-1;
            if(j-1<0) j = 0;
            chmin(dp[i][1], min(dp[j][0], dp[j][1])+p);
        }
    }
    cout << min(dp.back().front(), dp.back().back()) << '\n';
    // rep(i, n) {
    //     cout << " " << dp[i][0] << " " << dp[i][1] << '\n';
    // }
    return 0;
}