#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<unordered_map>
using namespace std;

typedef long long LL;

const int N = 100010;

int a[N];
int n,m;
LL sum;

int main()
{
    cin>>n>>m;
    for(int i = 1; i<=n; i++) cin>>a[i];
    a[n+1] = m;//边界
    int r = m/(n+1);
    int f,g,d;
    //分段代替枚举
    for(int i = 0; i<=n; i++)
    {
        f = i;
        for(int j = a[i]; j<a[i+1]; j+=d)//按照g值分段
        {
            g = j/r;
            int last = (g+1)*r-1;//g(x)值为g的最后一个数
            last = min(last,a[i+1]-1);//last值不能超过a[i + 1]
            LL cnt = last-j+1;
            LL t = abs(f-g);
            sum += t*cnt;
            d = cnt;
        }
    }
    cout<<sum;
    return 0;
}