#include <fstream>
#include <iostream>

using namespace std;

ifstream in ("deque.in");
ofstream out ("deque.out");
int d[5000010],a[5000010],n,k,f=0,l=0,i;
long long s;

void add (int k) {
    while (f<l&&a[d[l-1]]>=a[k]) l--;
    d[l++]=k;
}

int main () {
    in>>n>>k;
    for (i=0; i<k-1; i++) {
        in>>a[i];
        add (i);
    }
    for (; i<n; i++) {
        in>>a[i];
        add (i);
        if (i-d[f]>=k) f++;
        s+=a[d[f]];
    }
    out<<s<<"\n";
    return 0;
}