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*******************************************************************************/

#include <bits/stdc++.h>
#define ll long long
#pragma GCC optimize ("O3")
#define pb push_back
using namespace std;

int v[5000009];
signed main(){
    int n, k;cin >> n >> k;
    deque <int> dq;
    for(int i=1;i <= n;i++){
        cin >> v[i];
        if(i <= k){
            while(!dq.empty() && v[dq.back()] > v[i])dq.pop_back();
            dq.pb(i);
        }
    }
    ll ss = v[dq.front()];
    for(int i=k + 1;i <= n;i++){
        while(dq.front() <= i - k)dq.pop_front();
        while(!dq.empty() && v[dq.back()] > v[i])dq.pop_back();
        dq.pb(i);
        ss += v[dq.front()];
    }
    cout << ss;
    return 0;
}