#include<iostream>
#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int c[5000001], st=0, dr=-1;

void push_back(int x){
c[++dr]=x;
}

void pop_back(){
dr--;
}

void pop_front(){
st++;
}

int main()
{int n, k,v[5000001]  ;
long long sum=0;
    f>>n>>k;
     for(int i=0;i<n;i++)
        f>>v[i];
    for(int i=0;i<n;i++)
    {
        while(st<=dr && v[c[dr]]>v[i])
            pop_back();
        push_back(i);
        if(c[st]==i-k)
            pop_front();
        if(i>=k-1)
            sum+=v[c[st]];
    }
    g<<sum;
    return 0;
}