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#include <cstdio>
using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define FORD(i,a,b) for(int i=(b)-1;i>=(a);--i)
#define REP(i,n) FOR(i,0,n)
#define INT(x) int x; scanf("%d", &x)

int a[1000];

int main() {
	INT(n);
	INT(k);
	REP(i,n) scanf("%d", &a[i]);
	int r = 0;
	REP(i,n-1) if (a[i + 1] < a[i] - k) {
		r += a[i] - k - a[i + 1];
		a[i + 1] = a[i] - k;
	}
	FORD(i,1,n) if (a[i - 1] < a[i] - k) {
		r += a[i] - k - a[i - 1];
		a[i - 1] = a[i] - k;
	}
	printf("%d\n", r);
}