#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

const int MAX_LENGTH = 5000000;
const int MAX_VALUE = 10000000;

int aux[MAX_LENGTH + 1];

int main() {
    int numsLen, seqLen;
    fin >> numsLen >> seqLen;
    for (int i = 1; i <= numsLen; ++i) {
        fin >> aux[i];
    }
    deque<int> nums;
    nums.assign(aux + 1, aux + 1 + numsLen);
    long long sum = 0;
    for (deque<int>::iterator st = nums.begin(); st < nums.end() - seqLen + 1; ++st) {
        int minNumber = MAX_VALUE;
        for (deque<int>::iterator end = st; end <= st + seqLen - 1; ++end) {
            minNumber = min(*end, minNumber);
        }
        sum += minNumber;
    }
    fout << sum;
    return 0;
}
/*#include <iostream>
#include <deque>
using namespace std;

int main() {
    deque<int> first;
    int a[] = {3, 2, 4, 5};
    first.assign(a, a + 4);
    deque<int>::iterator it;
    it = first.begin();
    for (deque<int>::iterator it = first.begin(); it < first.end(); ++it) {
        cout << *it << ' ';
    }
    return 0;
}*/
/*
 9 3
 -7 9 2 4 -1 5 6 7 1
 =>
 -2
 
 1 1
 7
 =>
 7

 5 1
 1 2 3 4 5
 =>
 15

 5 5
 -1 -1 -1 -1 -1
 =>
 -1

 5 2
 1 -2 3 -4 5
 =>
 -12

 5 4
 5 -4 3 -2 1
 =>
 -8
 
 10 4
 -6 5 -2 3 4 11 -9 -2 -2 -3
 =>
 -46
 */