#include <bits/stdc++.h>

using namespace std;
deque < pair< int, int > >dq;
int x,n,k,i,s;
int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&x);
        while(!dq.empty()&&x<=dq.back().first)
        dq.pop_back();
        dq.push_back({x,i});
        while(dq.front().second<=i-k)
            dq.pop_front();
        if(i>=k) s+=dq.front().first;
    }
    printf("%d",s);

    return 0;
}