#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int N,v[5000005],k,a[5000005],i,left,right=1;long long s;int main(){f>>N>>k;for(i=1;i<=N;i++)f>>a[i];for(i=1;i<=N;i++){while(a[v[right]]>=a[i]&&right)right--;v[++right]=i;if(left>right)left=right;if(i>=k)s=s+a[v[left]];left+=(v[left]==i-k+1)}g<<s<<"\n";}