#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=2e5+10,INF=1e9;
int n,p,h[N],f[N][2];
signed main(){
    //freopen("climb.in","r",stdin);
    //freopen("climb.out","w",stdout);
    cin>>n>>p;
    for(int i=1;i<=n;i++) cin>>h[i];
    memset(f,0x3f,sizeof(f));
    f[1][0]=INF;f[1][1]=0;
    for(int i=2;i<=n;i++){
        f[i][0]=min(f[i-1][0]+max(0ll,h[i-1]-h[i]),min(f[i-1][0],f[i-1][1])+p);
        f[i][1]=min(f[i-1][1]+max(0ll,h[i]-h[i-1]),min(f[i-1][0],f[i-1][1])+p);
    }
    cout<<min(f[n][0],f[n][1])<<'\n';
    return 0;
}