#include <iostream>
#include <fstream>
#define inf 0x3f3f3f3f

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int N,K,pi,pf,sum,cmin=inf;
int main()
{
    in>>N>>K;
    int v[1+N];
    for(int i=1;i<=N;++i)
        in>>v[i];
    pi=1;
    pf=K;
    do{
        cmin=inf;
        for(int i=pi;i<=pf;++i)
            cmin=min(v[i],cmin);
        sum+=cmin;
        ++pi;
        ++pf;
    }while(pf<=N);
    out<<sum;
    return 0;
}