#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
ll t,n,k,i,j,x,y,sum;
deque<pair<ll,ll>>Q;
int main()
{   f>>n>>k;
    for(i=1;i<=n;i++){
        f>>x;
            while(Q.size()&&Q.back().se>=x){
                Q.pop_back();
            }
            while(Q.size()&&i-k+1>Q.front().fi){
                Q.pop_front();
            }
            Q.push_back({i,x});
            if (i>=k)
            sum=1ll*sum+Q.front().se;
    }
    g<<sum<<'\n';
    return 0;
}