#include <iostream>
#include <fstream>
#define maxn 5000010
#define inf 1000000000
using namespace std;

int N, K;
int A[maxn];
long long Sum;

int main() {
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin>>N>>K;
    int i, j, best;
    for (i = 0; i < N; ++i) {
        fin>>A[i];
    }
    for (i = 0; i < N - K + 1; ++i) {
        best = inf;
        for (j = 0; j < K; ++j) {
            if(A[i + j] < best)
                best = A[i + j];
        }
        Sum = Sum + best;
    }
    fout<<Sum;
    fin.close();
    fout.close();
    return 0;
}