#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int inf = 0x3f3f3f3f;
typedef long long ll;
int main()
{
int n,w,h;
int a[110];
while(~scanf("%d%d%d",&n,&w,&h)){
ll l ,r, sum;
l = r = sum =0;
memset(a,0,sizeof(a));
for(int i = w + 1; i <= w + n;i++){
scanf("%d",&a[i]);
sum += a[i];
}
if(sum < w*h){
printf("-1
");
continue;
}
int min1 = inf;
for(int i = 1; i <= 2*w + n;i++){
if(a[i] - h > 0)
r += a[i] - h;
else l += a[i] - h;
if(i >= w){
l = -l;
int temp = max(l,r);
min1 = min(min1,temp);
l = -l;
if(a[i-w+1]-h > 0)
r -= a[i-w+1]-h;
else l -= a[i-w+1] - h;
}
}
printf("%d
",min1);
}
return 0;
}