#include <cstdio>
#include <deque>
 
FILE* in;
FILE* out;
struct elem{
    int val;
    int tin;
};
 
std::deque<elem> a;
 
int main()
{
    in=fopen("deque.in","r");
    out=fopen("deque.out","w");
 
    int n,k,x;
 
    fscanf(in,"%d%d",&n,&k);
 
    long long rez=0;
 
    for(int i=1; i<=n; i++)
    {
        fscanf(in,"%d",&x);
 
        while(!a.empty() && x < a.back().val )
            a.pop_back();
        a.push_back(elem{x,i});
 
        if(i>=k)
        {
            rez+=a.front().val;
            if(a.front().tin==i-k+1)
                a.pop_front();
        }
    }
    fprintf(out,"%lld",rez);
 
    return 0;
}