思路：

貪心。

實現：

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 int a[100005];
 4 int main()
 5 {
 6     int n, m;
 7     while (cin >> n >> m)
 8     {
 9         for (int i = 1; i <= n; i++) cin >> a[i];
10         sort(a + 1, a + n + 1);
11         long long ans = 0;
 
12         int maxn = a[1], cnt = a[1] - 1;
13         for (int i = 2; i <= n; i++)
14         {
15             if (a[i] == a[i - 1])
16             {
17                 if (cnt) { ans += a[i]; cnt--; }
18                 else ans += a[i] - 1;
19             }
20             else 
21             {
 
22                 cnt += a[i] - maxn - 1;
23                 ans += maxn;
24                 maxn = a[i];
25             }
26         }
27         cout << ans << endl;
28     }
29     return 0;
30 }