#include<fstream>
#include<algorithm>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int i,u,p,k,n;
int v[5000005],d[5000005];
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--;
        u++;
        d[u]=i;
        if(d[u]-d[p]==k)
            p++;
        if(i>=k)
            s+=v[d[p]];
    }
    fout<<s;
    return 0;
}