#include <iostream>     // Input/output stream objects
#include <fstream>      // File stream objects
#include <sstream>      // String stream objects
#include <iomanip>      // Input/output manipulators
#include <string>       // String class and functions
#include <vector>       // Dynamic array
#include <list>         // Doubly linked list
#include <set>          // Set container
#include <map>          // Map container
#include <queue>        // Queue container
#include <stack>        // Stack container
#include <algorithm>    // Algorithms on sequences (e.g., sort, find)
#include <cmath>        // Mathematical functions
#include <climits>      // LLONG_MAX, LLONG_MIN
#include <ctime>        // Date and time functions
#include <cstdlib>      // General purpose functions (e.g., memory management)
#include <cstring>      // C-style string functions
#include <cctype>       // Character classification functions
#include <cassert>      // Assert function for debugging
#include <exception>    // Standard exceptions
#include <functional>   // Function objects
#include <iterator>     // Iterator classes
#include <limits>       // Numeric limits
#include <locale>       // Localization and internationalization
#include <numeric>      // Numeric operations (e.g., accumulate)
#include <random>       // Random number generators
#include <stdexcept>    // Standard exception classes
#include <typeinfo>     // Runtime type information
#include <utility>      // Utility components (e.g., std::pair)
#include <bitset>

using namespace std;

#define FOR(i, a, b) for(int i = a; i < (b); i++)
#define FORE(i, a, b) for(int i = a; i <= (b); i++)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
#define x first 
#define y second
#define mp make_pair
#define PI 3.141592653
#define compress(coord) sort(all(coord)), coord.resize(unique(all(coord)) - coord.begin())
const double eps = 1e-9; // x < eps (x <= 0) x < -eps (x < 0)
const ll inf = LLONG_MAX;

struct dqq {
    int mon;
    ll free;
};
const int N = 2e5 + 10;
int n, m, k;
vector<ll> fi(N), paid(N);
deque<dqq> dq;

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
    cin >> n >> m >> k;
    FORE (i, 1, n) cin >> fi[i];

    ll sumpaid = 0;
    FORE (i, 1, n) {
        while (!dq.empty() && i - dq.front().mon >= k) dq.pop_front();
        ll topaid = max(k - sumpaid, 0LL);
        if (topaid < fi[i]) {
            paid[i] = topaid;
            dq.push_back({i, fi[i] - paid[i]});
        }
        else {
            paid[i] = fi[i];
            topaid -= fi[i];
            while (!dq.empty() && topaid > 0) {
                ll fixpaid = min(topaid, dq.back().free);
                sumpaid += fixpaid;
                paid[dq.back().mon] += fixpaid;
                dq.back().free -= fixpaid; topaid -= fixpaid;
                if (dq.back().free == 0) dq.pop_back();
            }
        }
        sumpaid += paid[i] - paid[i-k+1];
    }
    ll ans = 0;
    FORE (i, 1, n) ans += paid[i];
    cout << ans << endl;
    return 0;
}