问题描述：

解题思路：

#include <iostream>
using namespace std;
int shumu, yushuan, l, r, ans;
int set = 1;
int main()
{
	cin >> shumu >> yushuan;
	cin >> l;
	while (cin >> r)
	{
		ans += (r - l) * set;
		l = r;
		set++;
	}
	cout << (ans + set * (yushuan - r));
}