#include <cstdio>

const int maxn=5000010;

int a[maxn], deque[maxn], i, k, n, first, last;
long long ans;

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

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

    for(i=1; i<=n; ++i) scanf("%d", &a[i]);

    first=1, last=0;
    for(i=1; i<=n; ++i) { while(first<=last && a[i]<= a[deque[last]]) --last;
                          deque[++last]=i;
                          if(deque[first]==i-k) ++first;
                          if(i>=k)
                          {
                              //printf("%d ", a[deque[first]]);
                              ans+=a[deque[first]];
                          }
                        }

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

    return 0;
}