#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long n,k,p,u,i,s;
long long d[5000001],v[5000001];
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--;
        u++;
        d[u]=i;
        if(i-d[p]==k)
            p++;
        if(i>=k)
            s+=v[d[p]];
    }
    fout<<s;
    return 0;
}