import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.StringTokenizer;
import java.util.TreeSet;

public class D {

	public static void main(String[] args) throws IOException {
		Scanner sc = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);

		char[] color = sc.next().toCharArray();
		int N = color.length;

		int[] nxt = new int[N];
		int[] prev = new int[N];

		for (int i = 0; i < N; i++) {
			nxt[i] = i + 1;
			prev[i] = i - 1;
		}

		TreeSet<Integer> set = new TreeSet<>();
		for (int i = 0; i < N; i++) {
			if(i > 0 && color[i] != color[i - 1]) {
				set.add(i);
				set.add(i - 1);
			}
		}

		int ans = 0;
		while(!set.isEmpty()) {
			ans++;
			TreeSet<Integer> tmp = new TreeSet<>();

			ArrayList<Integer> arr = new ArrayList<>();

			for(int x : set)
				arr.add(x);

			for (int i = 0; i < arr.size(); i++) {
				int cur = arr.get(i);
				if(!set.contains(cur))
					continue;
				int l = prev[cur];

				while(set.contains(cur)) {
					set.remove(cur);
					cur = nxt[cur];
				}
				
				if(l >= 0)
					nxt[l] = cur;
				if(cur < N)
					prev[cur] = l;
				
				if(l >= 0 && cur < N && color[l] != color[cur]) {
					tmp.add(l);
					tmp.add(cur);
				}
			}
			set = tmp;
		}

		out.println(ans);


		out.flush();
		out.close();
	}

	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}

		public Scanner(String file) throws FileNotFoundException {
			br = new BufferedReader(new FileReader(file));
		}

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}

		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}

		public String nextLine() throws IOException {
			return br.readLine();
		}

		public double nextDouble() throws IOException {
			String x = next();
			StringBuilder sb = new StringBuilder("0");
			double res = 0, f = 1;
			boolean dec = false, neg = false;
			int start = 0;
			if (x.charAt(0) == '-') {
				neg = true;
				start++;
			}
			for (int i = start; i < x.length(); i++)
				if (x.charAt(i) == '.') {
					res = Long.parseLong(sb.toString());
					sb = new StringBuilder("0");
					dec = true;
				} else {
					sb.append(x.charAt(i));
					if (dec)
						f *= 10;
				}
			res += Long.parseLong(sb.toString()) / f;
			return res * (neg ? -1 : 1);
		}

		public boolean ready() throws IOException {
			return br.ready();
		}

	}
}