#include <cstdio>
#include <vector>
using namespace std;

int n, k;
vector<int> A;
int main() {
    scanf("%d %d", &n, &k);
    A.resize(n);
    for(int i=0; i<n; ++i) scanf("%d", &A[i]);

    int result = 0;

    for(int i=0; i<n-1; ++i) if (A[i] > A[i+1] + k) {
        int diff = A[i] - k - A[i+1];
        result += diff;
        A[i+1] += diff;
    }        

    for(int i=n-1; i>0; --i) if (A[i] > A[i-1] + k) {
        int diff = A[i] - k - A[i-1];
        result += diff;
        A[i-1] += diff;
    }

    printf("%d\n", result);
    return 0;
}