#include<bits/stdc++.h>
using namespace std;
ifstream F("1.in");
ofstream G("1.out");
deque<int> d;
long long s;
int n,k,a[5000001],i;
int main()
{
    for(F>>n>>k,i=1;i<=n;F>>a[i++]);
    for(i=1;i<=n;++i) {
        for(;!d.empty()&&a[d.back()]>=a[i];d.pop_back());
        if(d.push_back(i),i-k>=d.front())
            d.pop_front();
        if(i>=k)
            s+=a[d.front()];
    }
    return G<<s,0;
}