#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define endl '\n'

int main(){
	ios::sync_with_stdio(false); cin.tie(0);
	int n, m, k;
	cin >> n >> m >> k;
	vector<int> a(2*m + n), res(2*m + n);
	set<int> s;
	for(int i=m; i<m+n; i++){
	    cin >> a[i];
	    s.insert(i);
    }
	int cur = 0;
	for(int i=1; i<m+n; i++){
	    // [i, i+m-1]
	    cur -= res[i-1];
	    auto it = s.lower_bound(i+m);
	    while(cur < k && it != begin(s) && *prev(it) >= i){
	        it = prev(it);
	        int j = *it;
	        ll amt = min(k - cur, a[j] - res[j]);
	        // cout << j-m+1 << ": " << amt << endl;
	        cur += amt;
	        res[j] += amt;
	        if(res[j] == a[j]){
	            it = s.erase(it);
	        }
	    }
	}
	cout << accumulate(res.begin(), res.end(), 0ll);
	
}