#include <bits/stdc++.h>
#define rep(i,l,r) for(int i=l; i<=r; i++)
#define IOS {cin.tie(0);cout.tie(0);ios::sync_with_stdio(0);}
using namespace std;

typedef long long ll;
typedef pair<int,int> P;

const int N = 400020;
int a[N], b[N], st[N], top, rem[N];

int main() {
    int n, m, k; scanf("%d%d%d", &n, &m, &k);
    rep (i, 1, n) {
        scanf("%d", &a[i]);
        rem[i] = a[i];
    }
    int now = 0;
    ll ans = 0;
    rep (i, 1, n+m-1) {
        if (i - m >= 1) {
            now -= b[i-m];
        }
        st[++top] = i;
        while (top && now < k) {
            int tmp = min(k - now, rem[st[top]]);
            rem[st[top]] -= tmp;
            b[st[top]] += tmp;
            if (rem[st[top]]== 0) top--;
            now += tmp;
            ans += tmp;
        }
    }
    cout << ans;
    return 0;
}