#include <fstream>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
long long s;
int n,i,x,t,v[5000015],frt[5000015],k;
int main(){
    fin>>n>>k;

    for(i=1;i<=n;i++)
        fin>>v[i];
    x=1;
    t=1;
    frt[1]=1;
    for(i=2;i<=n;i++){
        while(x<=t && v[i]<v[frt[t]])
            t--;
        frt[t++]=i;
        if(i-frt[x]==k)
            x++;
        if(i>=k)
            s+=v[frt[x]];
    }
    fout<<s<<" ";
}