#include<iostream>

using namespace std;

int n,T;
int t[200005];
int sum;
int main(){
	cin >> n >> T;
	for(int i = 1; i <= n; i++) cin >> t[i];
	for(int i = 1; i <= n; i++){
		if(t[i] - t[i - 1] <= 5){
			if(i != 1) sum += t[i] - t[i - 1];
			else sum += T;
		} else sum += T;
	}
	cout << sum << endl; 
	return 0;
}