#include <array>
#include <iostream>
#include <vector>

using namespace std;

int main() {
  int n, m, k;
  cin >> n >> m >> k;
  vector<int64_t> v;
  for(int i = 0; i < m-1; i++) v.push_back(0);
  for(int i = 0; i < n; i++) {
    int64_t x;
    cin >> x;
    v.push_back(x);
  }
  for(int i = 0; i < m-1; i++) v.push_back(0);
  vector<int64_t> paid(v.size());
  vector<array<int64_t, 2>> unused; 
  int64_t ret = 0;
  int64_t use = 0;
  for(int i = 0; i < v.size(); i++) {
    if(i >= m) use -= paid[i-m];
    unused.push_back({v[i], i});
    while(use < k && unused.size()) {
      auto [v, from] = unused.back(); unused.pop_back();
      if(from <= i-m) continue;
      int64_t take = min(k-use, v);
      paid[from] += take;
      use += take;
      ret += take;
      v -= take;
      if(v) unused.push_back({v, from});
    }
  }
  cout << ret << "\n";
}