#include <fstream>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
long long s;
int n,i,m,u,v[5000010],f[5000010],k;


int main(){
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    m=1;
    u=1;
    f[1]=1;
    for(i=2;i<=n;i++){
        while(m<=u && v[i]<v[f[u]])
            u--;
        f[++u]=i;
        if(i-f[m]==k)
            m++;
        if(i>=k)
            s+=v[f[m]];
    }
    fout<<s;
}