#include <fstream>

using namespace std;

#define MAX 5000100

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

int n,k,front,back;
int a[MAX], deque[MAX];
long long sol;

int main(){
    fin>>n>>k;
    for(int i=1;i<=n;++i) fin>>a[i];
    front=1;
    back=0;
    for(int i=1;i<=n;++i){
        while(front<=back && a[i]<=a[deque[back]]) --back;
        deque[++back]=i;
        if(deque[front]==i-k) front++;
        if(i>=k) sol+=a[deque[front]];
    }
    fout<<sol;


    return 0;
}