#include<bits/stdc++.h>
#define REP(x,y,z) for(int x=y;x<=z;x++)
#define FORD(x,y,z) for(int x=y;x>=z;x--)
#define MSET(x,y) memset(x,y,sizeof(x))
#define FOR(x,y) for(__typeof(y.begin()) x=y.begin();x!=y.end();x++)
#define F first
#define S second
#define MP make_pair
#define PB push_back
#define SZ size()
#define M 200005
void RI(){}
template<typename... T>
void RI( int& head, T&... tail ) {
    scanf("%d",&head);
    RI(tail...);
}
using namespace std;
typedef long long LL;
int n;
long long in[M],p;
long long dp[M][2];//fr,bk

LL calc()
{
	dp[1][0] = 0;
	dp[1][1] = (1LL)<<60;
	REP(i,2,n)
	{
		dp[i][0] = dp[i-1][0] + min(max(in[i]-in[i-1],0LL), p);
		dp[i][1] = dp[i-1][1] + min(max(in[i-1]-in[i], 0LL), p);

		dp[i][1] = min(dp[i][1], dp[i-1][0] + p);
		dp[i][0] = min(dp[i][0], dp[i-1][1] + p);
	}

	return min(dp[n][0], dp[n][1]);
}
int main()
{
	while(~scanf("%d %lld",&n,&p))
	{
		REP(i,1,n) scanf("%lld",&in[i]);
		printf("%lld\n", calc());


	}
	return 0;
}