#include <fstream>
int v[5000001];
int d[5000001];
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k, i, st, dr;
long long s;
int main(){
    fin>>n>>k;
    st=0;
    dr=-1;
    for (i=0;i<n;i++){
        fin>>v[i];
        if (st<=dr &&d[st]==i-k)
            st++;
        while(st<=dr && v[d[dr]]>=v[i])
            dr--;
        d[++dr]=i;
        if (i>=k-1)
            s+=v[d[st]];
    }
    fout<<s;
}