#include <cstdio>
#define MAXN 5000000

using namespace std;

int v[MAXN],dq[MAXN];

int main() {
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int st,dr,n,i,k;
    long long s;
    scanf("%d%d",&n,&k);
    s = 0;
    for( i = 0; i < n; i ++ )
      scanf("%d",&v[i]);
    st = 0;
    dr = -1;
    for( i = 0; i < n; i ++ ) {
      if( st <= dr && dq[st] == i - k )
        st ++;
      while( st <= dr && v[i] <= v[dq[dr]] )
        dr --;
      dq[++dr] = i;
      if( i >= k - 1 )
      s += v[dq[st]];
    }
    printf("%lld",s);
    return 0;
}