//Make CSP great again
//Vengeance
#include <bits/stdc++.h>
#define TASK "TESTCODE"
using namespace std;
const int N = 2e5;
int n, m, k;
long long a[N + 1];
stack<int> st;
struct FenwickTree
{
    long long tree[N + 1];
    void add(int pos, int val)
    {
        for (; pos <= n; pos |= pos + 1)
        {
            tree[pos] += val;
        }
    }
    long long sum(int pos)
    {
        long long ret = 0;
        for (; pos >= 0; pos = (pos & (pos + 1)) - 1)
        {
            ret += tree[pos];
        }
        return ret;
    }
    long long sum(int l, int r)
    {
        l = max(l, 0);
        r = min(r, n);
        return sum(r) - sum(l - 1);
    }
} tree;
void read()
{
    cin >> n >> m >> k;
    for (int i = 1; i <= n; ++ i)
    {
        cin >> a[i];
    }
}
void solve()
{
    long long res = 0;
    for (int i = 1; i <= n + m - 1; ++ i)
    {
        if (i <= n)
        {
            st.push(i);
        }
        while(!st.empty() && st.top() + m - 1 >= i)
        {
            long long s = tree.sum(i - m + 1, i);
            if (s >= k)
            {
                break;
            }
            int j = st.top();
            long long t = min(a[j], k - s);
            a[j] -= t;
            tree.add(j, t);
            res += t;
            if (a[j] == 0)
            {
                st.pop();
            }
        }
    }
    cout << res;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if (fopen(TASK".INP", "r"))
    {
        freopen(TASK".INP", "r", stdin);
        //freopen(TASK".OUT", "w", stdout);
    }
    int t = 1;
    bool typetest = false;
    if (typetest)
    {
        cin >> t;
    }
    for (int __ = 1; __ <= t; ++ __)
    {
        //cout << "Case " << __ << ": ";
        read();
        solve();
    }
}