#include <iostream>
#include <fstream>
using namespace std;
int d[5000005],v[5000005];
int main() {
    ifstream f("deque.in");
    ofstream g("deque.out");
    long long total=0;
    int first=1,last=0,n,k;
    f>>n>>k;
    for(int i=1;i<=n;++i)
        f>>v[i];
    for(int i=1;i<=n;++i){
        while(first<=last && v[i]<=v[d[last]])
            last--;
        last++;
        d[last]=i;
        if(d[first]==i-k)
            first++;
        if(i>=k)
            total+=v[d[first]];
    }
    g<<total;
    return 0;
}