#include <iostream>
using namespace std;
int v[5000000];
int d[5000000];
int st,dr;
istream in("deque.in");
ofstream out("deque.out");
int main(){
    int n,k,i;
    in>>n>>k;
    for(i=1; 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]=1;
        if(i>=k)
            s+=v[d[st]];
    }
    out<<s;
    return 0;
}