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

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

long long n,k,dr=-1,st,sum,i;
int s[5000001], d[5000001];

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