#include <iostream>
#include <fstream>
using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

int v[5000001],d[5000001];

int main(){
    int n,k,i,st,dr;
    long long s=0;

    in>>n>>k;
    st=0;
    dr=1;
    for(i=0;i<n;i++){
        in>>v[i];
        if(st<=dr&&d[st]==i-k)
            st++;
        while(st<=dr&&v[i]<=v[d[dr]])
            dr--;
        d[++dr]=i;
        if(i>=k-1)
            s+=v[d[st]];
    }
    out<<s;

    return 0;
}