#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
const int N = 1e5 + 5;

int arr[N], f[N][2];

int main()
{
    int n, c;
    scanf("%d %d", &n, &c);
    for (int i = 1; i <= n; ++i)
        scanf("%d", &arr[i]);
    memset(f, -0x3f, sizeof(f));
    f[1][0] = 0;
    f[1][1] = -arr[1] - c;
    for (int i = 2; i <= n; ++i)
    {
        f[i][0] = max(f[i-1][0], f[i-1][1]+arr[i]);
        f[i][1] = max(f[i-1][1], f[i-1][0]-arr[i]-c);
    }
    printf("%d", f[n][0]);
    return 0;
}