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#include <bits/stdc++.h>
int N,K,a[1009];
signed main(void) {
	scanf("%d %d",&N,&K);
	for(int i=1;i<=N;i++) {
		 scanf("%d",&a[i]);
	}
	long long ss=0;
	for(int i=1;i<=N;i++) {
		if(i<N&&a[i]<a[i+1]-K) {
			int dt=a[i+1]-a[i]-K;
			a[i]+=dt;
			ss+=dt;
			if(i>1) i-=2;
		}
		if(i>1&&a[i]<a[i-1]-K) {
			int dt=a[i-1]-a[i]-K;
			a[i]+=dt;
			ss+=dt;
		}
	}
	printf("%lld",ss);
}