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#include <bits/stdc++.h>
#define ssize(x) int(x.size())
#define all(x) x.begin(),x.end()
#define V vector
using namespace std;
typedef long long ll;
int mod = 1e09+7;
int add(int a, int b) { return a+b >= mod ? a+b-mod : a+b; }
int sub(int a, int b) { return add(mod-b, a); }
int mul(int a, int b) { return int(a*ll(b)%mod); }
int fpow(int a, int b = mod-2) {
    int res = 1;
    while(b) {
        if (b & 1) res = mul(res, a);
        b >>= 1, a = mul(a, a);
    }
    return res;
}
int divd(int a, int b) {
    return mul(a, fpow(b));
}
void answer() {
    int n, k; scanf("%d%d", &n, &k);
    V<int> t(n+1, 0);
    for (int i = 1; i <= n; ++i) scanf("%d", &t[i]);
    int result = 0;
    for (int i = 2; i <= n; ++i) {
        if (t[i-1]-t[i] > k) {
            result += t[i-1]-t[i]-k;
            t[i] += t[i-1]-t[i]-k;
        }
        int j = i;
        while(j > 1 && t[j-1] + k < t[j]) {
            result += t[j]-t[j-1]-k;
            t[j-1] += t[j]-t[j-1]-k;
            --j;
        }
    }
    printf("%d\n", result);
}
int main() {
    int T = 1; //scanf("%d", &T);
    for (++T; --T; ) answer();
    return 0;
}