#include "bits/stdc++.h"

using lint = int64_t;

using namespace std;

template<typename T> struct FT{
    vector<T> s;
    FT(int n) : s(n) {}
    void update(int pos, T dif){
        for(; pos < (int) s.size(); pos |= pos + 1) s[pos] += dif;
    }
    T query(int pos){
        T res = 0 ;
        for(; pos > 0; pos &= pos - 1) res += s[pos-1];
        return res;
    }
    T query(int a, int b){ //[a, b)
        return query(b) - query(a);
    }
};

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    set<int> ids;
    int n, m, k;
    cin>>n>>m>>k;
    vector<lint> cost(m-1 + n + m-1);
    for(int i = m-1; i < m-1 + n; i++){
        ids.insert(i);
        cin>>cost[i];
    }
    FT<lint> ft(cost.size());
    for(int i =m; i <= (int) cost.size(); i++){
        lint val = ft.query(i - m, i);
        while(val < k){
            if(ids.empty()) break;
            auto it = ids.lower_bound(i);
            if(it == ids.begin()) break;
            it--;
            int j = *it;
            lint dif = k - val;

            lint cur = min(dif, cost[j]);

            cost[j] -= cur;
            ft.update(j, cur);
            if(cost[j] == 0){
                ids.erase(j);
            }
            val = ft.query(i - m, i);
        }
    }
    cout<<ft.query(0, (int) cost.size())<<"\n";
    return 0;
}