using System.Text.RegularExpressions;

int n = int.Parse(Console.ReadLine());
string instr = Console.ReadLine();

int count = 0;

if (Regex.IsMatch(instr, @"000"))
{
    count += Regex.Matches(instr, @"000").Count * 2;
    instr = Regex.Replace(instr, @"000", "101");
}

if (Regex.IsMatch(instr, @"010"))
{
    count += Regex.Matches(instr, @"010").Count;
    instr = Regex.Replace(instr, @"010", "011");
}

if (Regex.IsMatch(instr, @"00"))
{
    count += Regex.Matches(instr, @"00").Count;
    instr = Regex.Replace(instr, @"00", "01");
}