1 #include<stdio.h>
 2 #include<string.h>
 3 #include<math.h>
 4 #include<algorithm>
 5 using namespace std;
 6 typedef long long ll ;
 7 const int inf = 0x3f3f3f3f ;
 8 int n , w , h ;
 9 
10 ll a[50010 * 3] ;
11 
12 int main ()
13 {
14     //freopen ("a.txt" , "r" , stdin ) ;
15     while (~ scanf ("%d%d%d" , &n , &w , &h) ) {
16         int sum = 0 ;
17         memset (a , 0 , sizeof(a)) ;
18         for (int i = w + 1; i <= n + w ; i++) {
19             scanf ("%d" , &a[i]) ;
20             sum += a[i] ;
21         }
22         int blog = w * h ;
23         if (sum < blog ) {
24             puts ("-1") ;
25             continue ;
26         }
27         int minn = inf ;
28         ll l = 0 , r = 0 ;
29         for (int i = 1  ; i <= n + w + w ; i++ ) {
30             a[i] - h < 0 ? l += a[i] - h : r += a[i] - h ;
31 
32             if (i >= w) {
33                 l = -l ;
34                 int temp = max (l , r) ;
35                 if (minn > temp ) {
36                     minn = temp ;
37                 }
38                 l = -l ;
39                 a[i - w + 1] - h < 0 ? l -= a[i - w + 1] - h : r -= a[i - w + 1] - h ;
40             }
41         }
42 
43      //   printf ("index = %d\n" , index) ;
44         printf ("%d\n" , minn ) ;
45     }
46     return 0 ;
47 }