#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
 
int n, k;
long long sum;
int numbers[5000000];
 
int sumOfMinimums() {
	
	for(int i = 1; i <= n; ++i) {
	    int mins = numbers[k];
	    for(int j = i; j <= k; ++j)
	        mins = min(mins, numbers[j]);
	    sum += mins;
	    ++k;
	}
	return sum;
	
}
 
int main() {
	fin >> n >> k;
	
	for(int i = 1; i <= n; ++i) {
	     fin >> numbers[i];
	}
	
	fout << sumOfMinimums();
	return 0;
}