#include <bits/stdc++.h>

using namespace std;

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)
#define unless(p) if(!(p))
#define until(p) while(!(p))

using ll = long long;

const int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1}, dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};

int N, P;
int H[252521];

int main(){
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    std::cin >> N >> P;

    for(int i=0;i<N;++i){
        std::cin >> H[i];
    }

    int cur = +1;
    ll res = 0ll;
    for(int i=0,j=0;i+1<N;i=j){
        ll cost = 0;
        while(j + 1 < N && cur * H[j] >= cur * H[j+1]){
            cost += abs(H[j + 1] - H[j]);
            ++j;
        }

        // std::cout << i << " -> " << j << std::endl;

        if(cur == -1){
            res += min(j + 1 == N ? 1ll * P : 1ll * P * 2, cost);
        }

        cur *= -1;
    }

    std::cout << res << std::endl;
}