#include <cstdio>
#include <deque>
#define Nmax 5000002
using namespace std;
deque <int> S;
int n , k ;

int sir[Nmax];

void citire()
{
    freopen ( "deque.in" , "r " , stdin);
    scanf("%d %d\n", &n, &k);
    for(int i = 0 ; i < n ; i++)
    {
        scanf("%d\n", &sir[i]);
    }
}
long long suma()
{
    long long sum = 0;
    for(int i = 0 ; i < n ; i++)
    {
        while(!S.empty() && sir[S.back()] > sir[i])///
            S.pop_back();
        S.push_back(i);
        if(S.front() <= i-k)
            S.pop_front();
        if(i >= k-1)
            sum+=sir[S.front()];
    }
    return sum;
}
int main()
{
    freopen("deque.out", "w" , stdout);
    citire();
    printf("%lld\n" , suma() );
    return 0;
}