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#include <iostream>
#include <cstdio>
#include <cstdlib>

int c;

void SKIP_WHITESPACE() {
    while (1) {
        c = fgetc(stdin);
        if (c != ' ' && c != '\n' && c != '\r')
            break;
    }
}

int READ_INT() {
    SKIP_WHITESPACE();
    int ret = c - '0';
    while (1) {
        c = fgetc(stdin);
        if (c < '0' || c > '9')
            break;
        ret = ret * 10 + c - '0';
    }
    return ret;
}

#define MAXN 1000

int n, k, i, sum, d;
int a[MAXN];

int main(int argc, char* argv[]) {
    std::ios_base::sync_with_stdio (false);


    n = READ_INT();
    k = READ_INT();

    for (i = 0; i < n; ++i) {
        a[i] = READ_INT();
    }

    for (i = 1; i < n; ++i) {
        if (a[i - 1] - a[i] > k) {
            sum += a[i - 1] - a[i] - k;
            a[i] = a[i - 1] - k;
        }
    }
    for (i = n - 2; i >= 0; --i) {
        if (a[i + 1] - a[i] > k) {
            sum += a[i + 1] - a[i] - k;
            a[i] = a[i + 1] - k;
        }
    }
    std::cout << sum << "\n";
    return EXIT_SUCCESS;
}