import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.bigint, std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static File _f;
void file_io(string fn) { _f = File(fn, "r"); }
static string[] s_rd;
T _RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T _RD(T = long)(File f) { while(!s_rd.length) s_rd = f.readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T[] _RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[] _RDA(T = long)(File f, T fix = 0) { auto r = f.readln.chomp.split.to!(T[]); r[] += fix; return r; }
T RD(T = long)() { if (_f.isOpen) return _RD!T(_f); else return _RD!T; }
T[] RDA(T = long)(T fix = 0) { if (_f.isOpen)  return _RDA!T(_f, fix); else return _RDA!T(fix); }

size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

void chmin(T)(ref T x, T y) { x = min(x, y); } void chmax(T)(ref T x, T y) { x = max(x, y); }
bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
long lcm(long x, long y) { return x * (y / gcd(x, y)); }

long mod = 10^^9 + 7;
//long mod = 998244353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }
void modpow(ref long x, long y) { if (!y) { x = 1; return; } auto t = x; x.modpow(y>>1); x.modm(x); if (y&1) x.modm(t); }

void main()
{
	auto n = RD!int;
	auto p = RDA!int;
	
	auto cnt = new int[](2);
	cnt[0] = n/2;
	cnt[1] = (n+1)/2;
	foreach (i; 0..n)
	{
		if (p[i] == 0) continue;
		auto j = p[i] % 2;
		--cnt[j];
	}

	auto dp = new int[][][](n+1, n+1, 2);
	foreach (i; 0..n+1)
	{
		foreach (j; 0..n+1)
			dp[i][j][] = -1;
	}
	dp[cnt[0]][cnt[1]][0] = 0;
	dp[cnt[0]][cnt[1]][1] = 0;
	foreach (i; 0..n)
	{
		auto ndp = new int[][][](n+1, n+1, 2);
		foreach (j; 0..n+1)
		{
			foreach (k; 0..n+1)
				ndp[j][k][] = -1;
		}
		foreach (j; 0..n+1)
		{
			foreach (k; 0..n+1)
			{
				foreach (l; 0..2)
				{
					if (dp[j][k][l] == -1) continue;
					if (p[i] != 0)
					{
						auto eo = p[i] % 2;
						auto num = dp[j][k][l] + (eo != l ? 1 : 0);
						if (ndp[j][k][eo] == -1)
							ndp[j][k][eo] = num;
						else
							ndp[j][k][eo].chmin(num);
						continue;
					}
					if (j != 0)
					{
						auto num = dp[j][k][l] + (l != 0 ? 1 : 0);
						if (ndp[j-1][k][0] == -1)
							ndp[j-1][k][0] = num;
						else
							ndp[j-1][k][0].chmin(num);
					}
					if (k != 0)
					{
						auto num = dp[j][k][l] + (l != 1 ? 1 : 0);
						if (ndp[j][k-1][1] == -1)
							ndp[j][k-1][1] = num;
						else
							ndp[j][k-1][1].chmin(num);
					}
				}
			}
		}
		dp = ndp;
	}
	debug writeln(dp);

	int ans = int.max;
	foreach (i; 0..2)
	{
		if (dp[0][0][i] != -1)
			ans.chmin(dp[0][0][i]);
	}

	writeln(ans);
	stdout.flush;
	debug readln;
}
