using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using SB = System.Text.StringBuilder;
using System.Numerics;
using static System.Math;
using Number = System.Int64;
namespace Program {
    public class Solver {
        Random rnd = new Random(0);

        public void Solve() {
            var n = ri;
            var a = Enumerate(n + 2, x => new int[n + 2]);
            for (int i = 0; i < n; i++) {
                var s = i == 0 ? "" : rs;
                for (int j = 0; j < i; j++) {
                    a[i + 1][j + 1] = s[j] - '0';
                    a[j + 1][i + 1] = 1 - a[i + 1][j + 1];
                }
            }
            /*
            n = 2000;
            a = Enumerate(n + 2, x => new int[n + 2]);
            for (int i = 1; i <= n; i++)
                for (int j = i + 1; j <= n; j++) {
                    var u = rnd.Next() % 2;
                    a[i][j] = u; a[j][i] = 1 - u;
                }
            */
            for (int i = 1; i <= n; i++) {
                a[i][0] = a[i][n + 1] = 1;
            }
            var lose = Enumerate(n + 2, x => new bitset());
            var adj = Enumerate(n + 2, x => new bitset());

            for (int i = 1; i <= n + 1; i++) {
                adj[i][i - 1] = true;
                lose[i][i - 1] = a[i][i - 1] == 0;
                for (int j = i - 1; j >= 1; j--) {
                    if (!adj[i][j]) continue;
                    if (a[i][j] == 0) lose[i][j] = true;
                    for (int k = 0; k < 32; k++) {
                        if (a[i][j] == 1)
                            adj[i].a[k] |= adj[j].a[k];
                        else adj[i].a[k] |= lose[j].a[k];
                    }
                }
            }
            var ans = 0;
            for (int i = 1; i <= n; i++)
                if (adj[i][0] && adj[n + 1][i]) ans++;
            Console.WriteLine(ans);

        }
        class bitset {
            public ulong[] a = new ulong[32];
            const int B = 64;
            public bool this[int index] {
                get { return (a[index / B] >> index & 1) == 1; }
                set {
                    if (value)
                        a[index / B] |= 1ul << index;
                    else a[index / B] &= ~(1ul << index);
                }
            }
        }



        const long INF = 1L << 60;
        int ri => sc.Integer();
        long rl => sc.Long();
        double rd => sc.Double();
        string rs => sc.Scan();
        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());

        static IEnumerable<int> Rep(int n) => Enumerable.Range(0, n);
        static IEnumerable<int> RRep(int n) => Enumerable.Range(0, n).Reverse();
        static T[] Enumerate<T>(int n, Func<int, T> f) {
            var a = new T[n];
            for (int i = 0; i < a.Length; ++i) a[i] = f(i);
            return a;
        }
        static public void Swap<T>(ref T a, ref T b) { var tmp = a; a = b; b = tmp; }
    }
}

#region main
static class Ex {
    static public string AsString(this IEnumerable<char> ie) { return new string(ie.ToArray()); }
    static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") {
        return string.Join(st, ie);
    }
    static public void Main() {
        Console.SetOut(new Program.IO.Printer(Console.OpenStandardOutput()) { AutoFlush = false });
        var solver = new Program.Solver();
        solver.Solve();
        Console.Out.Flush();
    }
}
#endregion
#region Ex
namespace Program.IO {
    using System.IO;
    using System.Text;
    using System.Globalization;

    public class Printer : StreamWriter {
        public override IFormatProvider FormatProvider => CultureInfo.InvariantCulture;
        public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
    }

    public class StreamScanner {
        public StreamScanner(Stream stream) { str = stream; }

        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof = false;

        private byte read() {
            if (isEof) return 0;
            if (ptr >= len) {
                ptr = 0;
                if ((len = str.Read(buf, 0, 1024)) <= 0) {
                    isEof = true;
                    return 0;
                }
            }
            return buf[ptr++];
        }

        public char Char() {
            byte b = 0;
            do b = read(); while ((b < 33 || 126 < b) && !isEof);
            return (char)b;
        }
        public string Scan() {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read()) sb.Append(b);
            return sb.ToString();
        }
        public string ScanLine() {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n' && b != 0; b = (char)read()) if (b != '\r') sb.Append(b);
            return sb.ToString();
        }
        public long Long() { return isEof ? long.MinValue : long.Parse(Scan()); }
        public int Integer() { return isEof ? int.MinValue : int.Parse(Scan()); }
        public double Double() { return isEof ? double.NaN : double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
}

#endregion


Measured memory_bytes: 35416