#include <bits/stdc++.h>

using namespace std;

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

const int DimMax=5000000;

int main()
{
long long n,k,st,dr,i,v[DimMax],dq[DimMax],s=0;
    in>>n>>k;
    st=0;
    dr=-1;
    for(i=0; i<n; i++)
    {
        in>>v[i];

        if(i>=k && dq[st]==i-k)
        {
            st++;
        }

        while(st<=dr && v[i]<=v[dq[dr]])
        {
            dr--;
        }
        dq[++dr]=i;
        if(i>=k-1)
        {
            s+=v[dq[st]];
        }
    }
    out<<s;
    return 0;
}