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#include <cstdio>

#ifdef LOCAL
    #define dbg(...) fprintf(stderr, __VA_ARGS__)
#else
    #define dbg(...)
#endif

using namespace std;

int hs[1000];
int totalzwir = 0;


int main() {
    int n, k;
    scanf("%d %d", &n, &k);
    for (int i = 0; i < n; ++i) {
        scanf("%d", &hs[i]);
        if (i == 0) continue;
        if (hs[i-1] - hs[i] > k) {
            // Current one is too low and needs to be raised up to hs[i-1] - k.
            totalzwir += hs[i-1] - hs[i] - k;
            hs[i] = hs[i-1] - k;
        }
        int curidx = i;
        while (curidx > 0 && hs[curidx] - hs[curidx-1] > k) {
            // current one is too high, and the previous needs to be raised.
            totalzwir += hs[curidx] - hs[curidx-1] - k;
            hs[curidx-1] = hs[curidx] - k;
            curidx--;
        }
    }
    printf("%d\n", totalzwir);
    return 0;
}