#include<algorithm>

 #include<iostream>

 #include<cstring>

 #include<cstdio>

 #include<cmath>

 using namespace std;

 typedef long long LL;

 const int maxn = +;

 int n;

 LL w, h;

 int arr[maxn*];

 void init() {

     memset(arr, , sizeof(arr));

 }

 int main() {

     while (scanf("%d%lld%lld", &n, &w,&h) ==  && n) {

         init();

         LL sum = ;

         for (int i = ; i < n; i++) {

             scanf("%d", arr + i+w);

             sum += arr[i+w];

         }

         if (sum < w*h) {

             printf("-1\n");

             continue;

         }

         //cntf:总共需要填入多少个方块，cntz:总共需要移出多少个方块，cnt保存连续w个的初始和

         LL cntz = ,cntf=w*h, cnt = ;

         LL ans = w*h;

         for (int i = w; i < *w+n; i++) {

             //计算新窗口的cntz,cntf,cnt；

             if (arr[i - w] - h>) cntz -= (arr[i - w] - h);

             else cntf -= (h - arr[i - w]);

             cnt -= arr[i - w];

             if (arr[i] - h > ) cntz += arr[i] - h;

             else cntf += h - arr[i];

             cnt += arr[i];

             LL tmp;

             if (w*h > cnt) tmp =cntf;

             else tmp = cntz;

             ans = min(ans, tmp);

         }

         printf("%lld\n", ans);

     }

     return ;

 }