#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

const long long MAX = 5100000;
const long long INF = 1LL << 60;
const long long mod = 1000000007LL;
//const long long mod = 998244353LL;

using namespace std;
typedef unsigned long long ull;
typedef long long ll;

ll dp1[200500];
ll dp2[200500];

int main()
{
    ll N, P; scanf("%lld %lld", &N, &P);
    vector<ll> h(N); for (ll i = 0; i < N; i++) scanf("%lld", &h[i]);
    for (ll i = 0; i <= N; i++) dp1[i] = INF, dp2[i] = INF;
    dp1[0] = 0;
    for (ll i = 1; i < N; i++) {
        chmin(dp1[i], dp1[i - 1] + max(h[i] - h[i - 1], 0LL));
        chmin(dp1[i], dp1[i - 1] + P);
        chmin(dp1[i], dp2[i - 1] + P);
        chmin(dp2[i], dp2[i - 1] + max(h[i - 1] - h[i], 0LL));
        chmin(dp2[i], dp2[i - 1] + P);
        chmin(dp2[i], dp1[i - 1] + P);
    }
    cout << min(dp1[N - 1], dp2[N - 1]) << endl;
    return 0;
}