#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int N,v[5000005],k,a[5000005],i;long long s;int main(){f>>N>>k;int left=1,right=0;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]];if(v[left] == i-k + 1) ++left;}g << s << "\n";}