#include <stdio.h>
struct stiva {long m;long p;};
long n,k,i,p,q,a;
long long sol;
stiva st[5000002]; 
int main(){
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%ld %ld",&n,&k);
    p=1;q=0;
    for (i=1;i<=n;++i){
        scanf("%ld",&a);
        while (a<st[q].m&&q>=p)q--;
        st[++q].m=a;
        st[q].p=i;
        while (i-st[p].p+1>k)p++;
        if (i>=k)sol+=st[p].m;
    }
    printf("%lld\n",sol);   
return 0;
}