#include <fstream>
#include <map>
using namespace std;
map <int, int>M;
int V[5000005];
long long int N,K,X,S;
ifstream fin("deque.in");
ofstream fout("deque.out");
int main(){
    fin>>N>>K;
    for(int i=1;i<=K;i++){
        fin>>V[i];
        M[V[i]]++;
    }
    S+=(M.begin()->first);
    for(int i=K+1;i<=N;i++){
        fin>>V[i];
        M[V[i-K]]--;
        M[V[i]]++;
        if(!M[V[i-K]])
            M.erase(M.find(V[i-K]));
        S+=(M.begin()->first);
    }
    fout<<S;
    return 0;
}