#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k, v[5000007];
long long s = 0;
int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i++){
        fin >> v[i];
    }
    for(int i = 1; i <= n-k+1; i++){
        int minim = 10000005;
        for(int j = i; j <= i+k-1; j++){
            if(v[j] < minim){
                minim = v[j];
            }
        }
        
        s = s+minim;
    }
    fout << s;
    return 0;
}