#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

ll MOD = 1000000007;
ll _MOD = 1000000009;
int INF = INT_MAX / 2;
double EPS = 1e-10;

int main() {
    int n, W, H;
    while (cin >> n >> W >> H) {
        int N = W + n + W;
        vector<int> A(N);
        ll sum = 0;
        for (int i = W; i < W + n; i++) {
            scanf("%d", &A[i]);
            sum += A[i];
        }
        if (sum < (ll)W * H) {
            cout << -1 << endl;
            continue;
        }
        vector<ll> x(N + 1), y(N + 1);
        for (int i = 1; i <= N; i++) {
            x[i] = x[i - 1];
            y[i] = y[i - 1];
            if (A[i - 1] < H) x[i] += H - A[i - 1];
            if (A[i - 1] > H) y[i] += A[i - 1] - H;
        }
        ll mini = LLONG_MAX;
        for (int i = 0; i + W <= N; i++) {
            ll a = x[i + W] - x[i], b = y[i + W] - y[i];
            mini = min(mini, max(a, b));
        }
        cout << mini << endl;
    }
}