#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

int gcd(int a, int b){
    while(b != 0){
        int t = b;
        b = a % b;
        a = t;
    }
    return a;
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int n, k, p, q;
    cin >> n >> k >> p >> q;
    vector<int> arr;
    vector<int> duparr(2*n);
    for(int i = 0; i < n; i++){
        int tmp;
        cin >> tmp;
        arr.push_back(tmp);
        duparr[i] = arr[i];
        duparr[i+n] = arr[i];
    }

    vector<ll> pSubrows(n);
    ll currsum = 0;
    for(int i = 0; i < n+q-1; i++){
        currsum+=duparr[i];
        if(i >= q-1){
            pSubrows[i-q+1] = currsum;
            currsum-=duparr[i-q+1];
        }
    }

    // this will store the index of the top-left element of the subrectangle
    int buckets = gcd(n,k);
    int bucketLen = n/buckets;
    vector<vector<ll>> subrows(buckets, vector<ll>(bucketLen));
    vector<vector<int>> sumToIndex(buckets, vector<int>(bucketLen));
    for(int bucket = 0; bucket < buckets; bucket++){
        int idx = bucket;
        for(int i = 0; i < bucketLen; i++){
            subrows[bucket][i] = pSubrows[idx];
            sumToIndex[bucket][i] = idx;
            idx+=k;
            idx%=n;
        }
    }
    vector<vector<ll>> subrowSums(buckets, vector<ll>(bucketLen));
    for(int bucket = 0; bucket < buckets; bucket++){
        long totsum = 0;
        for(int i = 0; i < bucketLen; i++) totsum+=subrows[bucket][i];
        int mult = p/bucketLen;
        int extra = p%bucketLen;
        long currsum2= totsum*mult;
        for(int i = 0; i < bucketLen+extra; i++){
            if(i >= extra){
                subrowSums[bucket][(i-extra)%bucketLen] = currsum2;
                currsum2-=subrows[bucket][(i-extra)%bucketLen];
            }
            currsum2+=subrows[bucket][i%bucketLen];
        }
    }

    // now we check which subrow sums actually exist in the grid
 

    bool all = false;
    vector<int> markers(2*n, 0);
    int start = 0;
    for(int i = 0; i < n-p+1; i++){
        int end = (start+(n-q+1));
        if(end-start >= n){
            all = true;
            break;
        }
        markers[start]++;
        markers[end]--;
        start+=k;
        start%=n;
    }
    vector<int> exists;
    int startVal = 0;
    for(int i = 0; i < 2*n; i++){
        startVal+=markers[i];
        exists.push_back(startVal);
    }
    vector<bool> elements(n, false);
    for(int i = 0; i < n; i++){
        if(exists[i] != 0 || exists[i+n] != 0){
            elements[i] = true;
        }
    }

    ll ans = LONG_MIN;
    for(int i = 0; i < buckets; i++){
        for(int j = 0; j < bucketLen; j++){
            if(all || elements[sumToIndex[i][j]]) ans = max(ans, subrowSums[i][j]);
        }
    }

    cout << ans << endl;
}