#pragma GCC optimize("Ofast")
#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cassert>
#include <chrono>
#include <random>
#include <set>
#include <utility>
#include <array>
#include <bitset>
#include <unordered_set>
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) {
    return (ull)rng() % B;
}
inline double time() {
    return static_cast<long double>(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count()) * 1e-9;
}

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n,m; cin >> n >> m;
    ll k; cin >> k;
    vector<ll> a(n);
    for (int i = 0; i < n; ++i) {
        cin >> a[i];
    }
    vector<ll> dp(n+1, 1e18);
    dp[0] = 0;
    for (int i = 0; i < n; ++i) {
        ll mi = a[i], mx = a[i];
        for (int j = 0; j < m and i+j < n; ++j) {
            mi = min(mi, a[i+j]);
            mx = max(mx, a[i+j]);
            dp[i+j+1] = min(dp[i+j+1], dp[i]+k+(mx-mi)*(j+1));
        }
    }
    cout << dp[n] << endl;
}