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

ifstream f("deque.in");
ofstream g("deque.out");

int n,k,v[5000002],dq[5000002];

int main()
{
    long long i,frontt,backk,s=0;
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>v[i];
    frontt=1;
    backk=0;
    for(i=1;i<=n;i++)
    {
        while(frontt<=backk && v[i]<=v[dq[backk]])
            backk--;
        backk++;
        dq[backk]=i;
        if(dq[frontt]==i-k)
            frontt++;
        if(i>=k)
            s+=v[dq[frontt]];
    }
    g<<s;
    return 0;
}