#include<bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int v[5000005],dequee[5000005];
long long n,ans,k;

int main()
{
    fin>>n>>k;
    for(long long i=1;i<=n;i++)
        fin>>v[i];
    long long st=1,dr=0;
    for(long long i=1;i<=n;i++)
    {
        while(v[i]<=v[dequee[dr]]&&st<=dr)
            dr--;
        dequee[++dr]=i;
        if(dequee[st]==i-k)
            st++;
        if(i>=k)
            ans+=v[dequee[st]];
    }
    fout<<ans;
}