#include<stdio.h>
#include<deque>
#include<vector>
using namespace std;
int n,i,k;
long long x,s;
deque < pair<long long,int> > Q;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d%d",&n,&k);
    for(i=0;i<n;i++)
    {
        scanf("%lld",&x);
        while(!Q.empty()&&Q.back().first>x)
            Q.pop_back();
        Q.push_back(make_pair(x,i));
        if(Q.front().second==i-k)
            Q.pop_front();
        if(i+1>=k)
            s+=Q.front().first;
    }
    printf("%lld\n",s);
    return 0;
}