#include <fstream>

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

int v[5000001],coada[5000001];

int main(){
    int inc=1,sf=1,i,k,n;
    long long s=0;
    cin>>n>>k;
    for(i=1;i<=n;i++)
        cin>>v[i];
    coada[1]=1;
    for(i=2;i<=k;i++){
        while(v[i]<v[coada[sf]] && inc<=sf)
            sf--;
        sf++;
        coada[sf]=i;
    }
    s+=v[coada[inc]];
    for(;i<=n;i++){
        if(coada[inc]<=i-k)
            inc++;
         while(v[i]<v[coada[sf]] && inc<=sf)
            sf--;
        sf++;
        coada[sf]=i;
        s+=v[coada[inc]];
    }
    cout<<s;
    return 0;
}