#include <iostream>
#include <fstream>
using namespace std;
long long a[5000001];
ifstream in("deque.in");
ofstream out("deque.out");
int main(){

long long  n, k;
in >> n >> k;
for(long long  i = 0; i < n; i++){
    in >> a[i];
}

long long Min = 1e7+1;
for(long long  i = 0; i < k; i++){
    if(a[i] < Min)
        Min = a[i];
}
long long s = Min;
for(long long  i = 1; i <= n-k; i++){
    Min = 1e7+1;
    bool ok = false;
    for(int j = i; j < i+k; j++){
        ok = true;
        Min = min(Min,a[j]);
    }
    if(ok == true){
        s+=Min;
    }
}

out << s;
in.close();
out.close();
    return 0;
}