import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); } bool DEBUG = 0; 
void log(A ...)(lazy A a){ if(DEBUG) print(a); }
void print(){ writeln(""); } void print(T)(T t){ writeln(t); } void print(T, A ...)(T t, A a){ write(t, " "), print(a); }
string unsplit(T)(T xs){ return xs.array.to!(string[]).join(" "); }
string scan(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
T scan(T)(){ return scan.to!T; } T[] scan(T)(int n){ return n.iota.map!(i => scan!T()).array; }
T lowerTo(T)(ref T x, T y){ if(x > y) x = y; return x; } T raiseTo(T)(ref T x, T y){ if(x < y) x = y; return x; }

// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //

void solve(){
    int n = scan!int;
    long[] as = scan!long(n + 1);
    log("as:", as);

    long[] ls;
    long u = 1;
    foreach(i, a; as){
        ls ~= u;
        u = (u - a) * 2;
        if(u > (1L<<60)) u = 1L<<60;
    }
    log("ls:", ls);

    long x = 0;
    long ans = 0;
    foreach_reverse(i, a; as){
        long l = ls[i];
        log("i:", i, "a:", a, "l:", l);
        if(x + a <= l){
            x += a;
            ans += x;
            log("1.", "x:", x, "ans:", ans);
        }
        else if((x + 1) / 2 + a <= l){
            x = l;
            ans += l;
            log("2.", "x:", x, "ans:", ans);
        }
        else{
            "-1".print;
            return;
        }
    }
    ans.print;
}
