#include <fstream>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k;
long long sum;
int a[5000005];
int de[5000005];
int main()
{   int fr,bc;
    fr=1; bc=0;
    int i;
    fin>>n>>k;
    for(i=1;i<=n;++i)
    { fin>>a[i];
        while( fr<=bc && a[i]<=a[de[bc]] )   bc--;
        de[++bc]=i;
        if(de[fr]==i-k) fr++;
        if(i>=k) sum+=a[de[fr]];
    }
    fout<<sum;
    return 0;
}