#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int N;
long P;
long H[2<<17];
main()
{
	cin>>N>>P;
	for(int i=0;i<N;i++)cin>>H[i];
	long A=0,B=P;
	for(int i=1;i<N;i++)
	{
		long nA,nB;
		nA=A+max(0L,H[i]-H[i-1]);
		nB=B+max(0L,H[i-1]-H[i]);
		nB=min(nB,A+P);
		nA=min(nA,B+P+max(0L,H[i]-H[i-1]));
		nA=min(nA,A+P);
		nB=min(nB,B+P);
		A=nA;
		B=nB;
	}
	cout<<min(A,B)<<endl;
}