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// Author: Bartek Knapik

#include <cstdio>

const int MAXN = 1000+9;

long long l[MAXN];

long long process(int n, int k)
{
    bool changed = true;
    long long l_diff, r_diff, diff, res;
    
    res = 0LL;
    
    while (changed)
    {
        changed = false;
        for (int i = 0; i < n; ++i)
        {
            l_diff = (i == 0) ? 0 : l[i - 1] - l[i];
            r_diff = (i == n - 1) ? 0 : l[i + 1] - l[i];
            diff = l_diff > r_diff ? l_diff : r_diff;
            if (diff > k)
            {
                res += diff - k;
                l[i] += diff - k;
                changed = true;
            }
        }
    }
    return res;
}

int main()
{
    int n, k;
    scanf("%d%d", &n, &k);
    for (int i = 0; i < n; ++i)
        scanf("%lld", &l[i]);
    
    printf("%lld\n", process(n, k));
    return 0;
}