#include <iostream>
#include <fstream>

using namespace std;
const int N = 5000001;
int v[N];
int d[N];
ifstream in( "deque.in" );
ofstream out( "deque.out" );

int main(){
    int st,dr,n,k,i;
    long long s;
    s=0;
    in >> n >> k;
    for(i=0; i<n; i++){
        in >> 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=s+v[d[st]];
    }
    out << s;
    return 0;
}