#include<bits/stdc++.h>
using namespace std;
ifstream F("deque.in");
ofstream G("deque.out");
#define N 5000005
int n,k,i,j,a[N],l,r;
deque<int> q;
long long s;
int main()
{
    for(F>>n>>k,i=1;i<=n;++i) {
        for(F>>a[i];!q.empty()&&a[q.back()]>=a[i];q.pop_back());
        q.push_back(i);
        if(i-q.front()==k)
            q.pop_front();
        if(i>=k)
            s+=a[q.front()];
    }
    return G<<s,0;
}