import std.stdio, std.string, std.conv;
import std.array, std.algorithm;

void main(){
    auto l = readln.strip.to!int;
    auto arr = readln.strip.split.map!(to!int).array;
    uint ans;
    if(l == 1){ans = arr[0];}
    while(arr.length > 1){
        int max, pos;
        foreach(i, x; arr){
            if(max < x){
                max = x;
                pos = i.to!int;
            }else if(max == x){
                int sum = (pos-1 > 0 ? arr[pos-1]:0) + arr[pos] + (pos+1 < arr.length ? arr[pos+1]:0);
                int currSum = (i-1 > 0 ? arr[i-1]:0) + arr[i] + (i+1 < arr.length ? arr[i+1]:0);
                if(sum < currSum){
                    max = x;
                    pos = i.to!int;
                }
            }
        }
        ans += max;
        
        if(pos+1 < arr.length){
            arr = arr.remove(pos+1);
        }
        arr = arr.remove(pos);
        if(pos-1 >= 0){
            arr = arr.remove(pos-1);
        }
    }
    
    ans.writeln;
}