#include <cstdio>

 const int MAXN = ;

 int n, m, h = , t = , ans = ~( << );

 int q[MAXN], a[MAXN], f[MAXN];

 inline int min(int x, int y)

 {

     return x < y ? x : y;

 }

 int main()

 {

     int i;

     scanf("%d %d", &n, &m);

     for(i = ; i <= n; i++) scanf("%d", &a[i]);

     for(i = ; i <= n; i++)

     {

         while(h <= t && q[h] < i - m) h++;

         f[i] = f[q[h]] + a[i];

         while(h <= t && f[q[t]] > f[i]) t--;

         q[++t] = i;

      }

      for(i = n - m + ; i <= n; i++) ans = min(ans, f[i]);

      printf("%d\n", ans);

      return ;

 }