#include<bits/stdc++.h>
using namespace std;
#define ALL(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define mod 1000000007
using ll=long long;
const int INF=1000000000;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

struct IOSetup{
    IOSetup(){
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout<<fixed<<setprecision(12);
    }
} iosetup;

template<typename T1,typename T2>
ostream &operator<<(ostream &os,const pair<T1,T2>&p){
    os<<p.first<<" "<<p.second;
    return os;
}

template<typename T>
ostream &operator<<(ostream &os,const vector<T>&v){
    for(int i=0;i<(int)v.size();i++) os<<v[i]<<(i+1==v.size()?"":" ");
    return os;
}


signed main(){
    int n;ll p;cin>>n>>p;
    vector<ll> h(n);rep(i,n) cin>>h[i];
    ll dp[n+1][2];
    rep(i,n+1)rep(j,2)dp[i][j]=LINF;
    dp[0][0]=0;
    rep(i,n){
        rep(j,2){
            ll pre=(i==0?h[0]:h[i-1]);
            // 区間開始
            chmin(dp[i+1][j],dp[i][0]+p);
            chmin(dp[i+1][j],dp[i][1]+p);

            if(j==0)chmin(dp[i+1][j],dp[i][j]+max(h[i]-pre,0ll));
            else    chmin(dp[i+1][j],dp[i][j]+max(pre-h[i],0ll));
        }
    }
    cout<<min(dp[n][0],dp[n][1])<<endl;
    return 0;
}