#include <bits/stdc++.h>
#include <iomanip>
using namespace std;

int v[5000005],minn[5000005];


signed main() {
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    int n,k,rez=0;
    cin >> n >> k;
    for(int i=1;i<=n;i++)
    {
        cin >> v[i];
    }
    deque<int> dq;
    for(int i=0;i<k;i++)
    {
        while(!dq.empty() && v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
    }
    minn[0]=v[dq.front()];
    for(int i=k;i<=n;i++)
    {
        if(dq.front()<=i-k)
            dq.pop_front();

        while(!dq.empty() && v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
        minn[i-k+1]=v[dq.front()];
    }
    for(int i=1;i<=n-k+1;i++)
    {
        rez+=minn[i];
    }
    cout << rez;
    return 0;
}