#include <cstdio>
using namespace std;

FILE *f = fopen("deque.in", "r");
FILE *g = fopen("deque.out", "w");

const int NMAX = 5000001;

int N, K, x;
int v[NMAX], DQ[NMAX];

long long solve()
{
    fscanf(f, "%d%d", &N, &K);
    for(int i = 1; i <= N; i++)
        fscanf(f, "%d", &v[i]);
    int f = 1, b = 0;
    for(int i = 1; i < K; i++)
    {
        //
        while(f <= b && v[i] <= v[DQ[b]])
            b--;
        //
        DQ[++b] = i;
        if(DQ[f] == i - K)
            f++;
    }
    long long S = 0;
    for(int i = K; i <= N; i++)
    {
        while(f <= b && v[i] <= v[DQ[b]])
            b--;
        //
        DQ[++b] = i;
        if(DQ[f] == i - K)
            f++;
        S += v[DQ[f]];
    }
    return S;
}

int main()
{
    fprintf(g, "%lld", solve());
    return 0;
}