#include <bits/stdc++.h>

#define FOR(i, x, n) for(int i = x; i < n; i++)
#define F0R(i, n) FOR(i, 0, n)
#define ROF(i, x, n) for(int i = n - 1; i >= x; i--)
#define R0F(i, n) ROF(i, 0, n)

#define IOS ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

using namespace std;

typedef long long LL;

const int N = 2e5 + 7;

LL n, m, k;
LL ns[N], bought[N];
stack<int> keep;

int main() {
    cin >> n >> m >> k;

    LL sumbought = 0;
    F0R(i, m - 1) {
        keep.push(i);
    }

    LL ans = 0;
    FOR(i, m - 1, n + m - 1 + (m - 1)) {
        if (i < n + m - 1) cin >> ns[i];
        keep.push(i);

        if (i >= m) sumbought -= bought[i - m];
        
        while(sumbought < k) {
            if (keep.empty() || keep.top() < i - m + 1) break;

            if (sumbought + ns[ keep.top() ] > k) {
                bought[keep.top()] += k - sumbought;
                ns[ keep.top() ] -= (k - sumbought);
                ans += k - sumbought;
                sumbought = k;
            }

            else {
                sumbought += ns[ keep.top() ];
                bought[ keep.top() ] += ns[ keep.top() ];
                ans += ns[keep.top()];
                ns[ keep.top() ] = 0;
                keep.pop();
            }
        }
    }

    cout << ans << endl;
}