Problem:
Score : 300 points

Problem Statement

In a public bath, there is a shower which emits water for T seconds when the switch is pushed.

If the switch is pushed when the shower is already emitting water, from that moment it will be emitting water for T seconds.
Note that it does not mean that the shower emits water for T additional seconds.

N people will push the switch while passing by the shower.
The i-th person will push the switch t_i seconds after the first person pushes it.

How long will the shower emit water in total?

Constraints

1 ≤ N ≤ 200,000

1 ≤ T ≤ 10^9

0 = t_1 < t_2 < t_3 < , ..., < t_{N-1} < t_N ≤ 10^9

T and each t_i are integers.

Input

Input is given from Standard Input in the following format:

N T
t_1 t_2 ... t_N

Output

Assume that the shower will emit water for a total of X seconds. Print X.

Sample Input 1

2 4
0 3

Sample Output 1

7

Three seconds after the first person pushes the water, the switch is pushed again and the shower emits water for four more seconds, for a total of seven seconds.

Sample Input 2

2 4
0 5

Sample Output 2

8

One second after the shower stops emission of water triggered by the first person, the switch is pushed again.

Sample Input 3

4 1000000000
0 1000 1000000 1000000000

Sample Output 3

2000000000

Sample Input 4

1 1
0

Sample Output 4

1

Sample Input 5

9 10
0 3 5 7 100 110 200 300 311

Sample Output 5

67

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define rep(i, n) for(int i=0; i<n; i++)
#define repr(i, s, e) for(int i=s; i>=e; i--)
#define reps(i, s, e) for(int i=s; i<e; i++)
#define inf 1e18
#define vsort(v) sort(v.begin(), v.end())
#define vsortr(v) sort(v.begin(), v.end(), greater<ll>())
#define sz(x) x.size()
#define ceil(a, b) (a+b-1)/b
#define ok cout << "ok" << endl;
using namespace std;
using ll = long long;
template<typename T> inline bool chmax(T &a, T b){ if(a<b){ a=b; return true; } return false; }
template<typename T> inline bool chmin(T &a, T b){ if(b<a){ a=b; return true; } return false; }
template<typename T> T gcd(T a, T b){ if(b==0) return a; return gcd(b, a%b); }
template<typename T> T lcm(T a, T b){ return a*b/gcd(a, b); }
template<typename T> void vdebug(vector<T> v){ for(auto vv : v){ cout << vv << " "; } cout << endl; }
template<typename T> void adebug(T arr[], int n){ rep(i, n){ cout << arr[i] << " "; } cout << endl; }
void ans(bool b){ if(b) cout << "Yes" << endl; else cout << "No" << endl; }
void ans2(bool b){ if(b) cout << "YES" << endl; else cout << "NO" << endl; }
int keta(ll num){ int k=0; while(num>0){ num/=10; k++; } return k; }
int dx[] = {1, -1, 0, 0, 1, -1, 1, -1};
int dy[] = {0, 0, 1, -1, 1, -1, -1, 1};


int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);

    ll n, T, t, last=0;
    cin >> n >> T;

    ll res = 0;
    rep(i, n){
        cin >> t;
        if(i==0){
            last = t;
            continue;
        }
        res += min(T, t-last);
        last = t;
    }
    res += T;

    cout << res << endl;

    return 0;
}