#include <fstream>
#include <set>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,a[5000011];

multiset<int> v;
multiset<int>::iterator it;

int main(void){
    register int i,j,x,p=0;
    register long long sum=0;

    f>>n>>k>>a[1];
    v.insert(a[1]),p=1;
    for(i=2;i<=k;i++)
        f>>a[i],v.insert(a[i]);
    sum=*v.begin();
    for(i=k+1;i<=n;i++){
        f>>a[i];
        v.insert(a[i]);
        v.erase(a[p]);
        p++;
        //g<<*v.begin()<<"\n";
        sum+=*v.begin();
    }

    g<<sum;
    return 0;
}