#include <bits/stdc++.h>
using namespace std;
#define ll                 long long 
#define all(v)             v.begin(), v.end()
ll ceil2(ll a, ll b) {
return (a + b - 1) / b;
}
// #include <ext/pb_ds/assoc_container.hpp> 
// #include <ext/pb_ds/tree_policy.hpp> 
// using namespace __gnu_pbds; 
// #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> 



void solve(){
    int n, m;cin>>n>>m;
    ll v[5000005];
    for(int i=0 ;i<n; i++){
        cin>>v[i];
    }
    multiset<int> s;
    for(int i=0 ;i<m; i++){
        s.insert(v[i]);
    }
    ll sum=*s.begin();
    for(int i=m; i<n; i++){
        s.erase(v[i-m]);
        s.insert(v[i]);
        sum+=*s.begin();
    }
    cout<<sum;
    
    
}


int main(){
    freopen("deque.in", "rt", stdin);
	freopen("deque.out", "wt", stdout);
   ios_base::sync_with_stdio(false); cin.tie(NULL);
//    ll t;cin>>t;while(t--){solve();cout<<endl;}
    solve();
}