#include<bits/stdc++.h>
#define FL(i,a,b) for(ll i=(a);i<=(b);i++)
#define FR(i,a,b) for(ll i=(a);i>=(b);i--)
#define ll long long
using namespace std;
const ll MAXN = 2e5 + 10;
ll n,V;
ll h[MAXN];
ll f[MAXN][2];
signed main(){
	scanf("%lld%lld",&n,&V);
	FL(i,1,n) scanf("%lld",&h[i]);
	memset(f,0x3f,sizeof(f));
	f[1][1]=0,f[1][0]=V;
	FL(i,1,n){
		f[i+1][0]=min(f[i][0]+max(0ll,h[i]-h[i+1]),min(f[i][0],f[i][1])+V);
		f[i+1][1]=min(f[i][1]+max(0ll,h[i+1]-h[i]),min(f[i][0],f[i][1])+V);
	}
	printf("%lld\n",min(f[n][0],f[n][1]));
}