#include <bits/stdc++.h>

using namespace std;

//#define FILE_IO

typedef long long LL;

LL N, K;
LL v[100005];
LL dp[100005];

int main()
{
    #ifdef FILE_IO
    freopen("1.in", "r", stdin);
    freopen("1.out", "w", stdout);
    #endif

    scanf("%lld%lld", &N, &K);
    for(LL i = 1; i <= N; i++)
        scanf("%lld", &v[i]);

    for(LL i = 1; i <= N; i++)
        dp[i] = 1LL << 60;

    for(LL i = 1; i <= N; i++)
        dp[min(i + K, N)] = min(dp[min(i + K, N)], dp[max(i - K - 1, 0LL)] + v[i]);

    LL ans = dp[N];
    printf("%lld\n", ans);

    return 0;
}