#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,i,p,u,v[5000010],D[5000010],k;
long long s;
int main(){
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    p=1;
    u=1;
    D[1]=1;
    for(i=2;i<=n;i++){
        while(p<=u&&v[i]<v[D[u]])
            u--;
        D[++u]=i;
        if(i-D[p]==k)
            p++;
        if(i>=k)
            s+=v[D[p]];
    }
    fout<<s;
}