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

ifstream in("deque.in");
ofstream out("deque.out");
int v[5000001];
int d[5000001];
int main()
{   int n,k;
    in>>n>>k;
    for(int i=1;i<=n;i++) in>>v[i];
    int inc=1, sf=0;
    long long s=0;
    for(int i=1;i<=n;i++){
        while(inc<=sf and v[d[sf]]>v[i]) sf--;
        d[++sf] = i;
        if(d[inc] == i-k) inc++;
        if(i>=k) s+=v[d[inc]];
    }
    out<<s;
    return 0;
}