#include <iostream>
#include <fstream>
using namespace std;

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

const int N=5000000;
int v[N];
int d[N];

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