void main() {
	auto S = rs.to!(dchar[]);
	auto k = S.length;
	bool flag = true;
	while(flag) {
		debug S.writeln;
		if(S.length == 0 || S == "0" || S == "1") { flag = false; break; }
		foreach(i; 0..S.length-1) {
			if(S[i] != S[i+1]) {
				debug writefln("%s, %s", S[0..i], S[i+2..$]);
				S = S[0..i] ~ S[i+2..$];
				break;
			}
			if(i == S.length-2) flag = false;
		}
	}
	(k - S.length).writeln;
}

// ===================================

import std.stdio;
import std.string;
import std.functional;
import std.algorithm;
import std.range;
import std.traits;
import std.math;
import std.container;
import std.bigint;
import std.numeric;
import std.conv;
import std.typecons;
import std.uni;
import std.ascii;
import std.bitmanip;
import core.bitop;

T readAs(T)() if (isBasicType!T) {
	return readln.chomp.to!T;
}
T readAs(T)() if (isArray!T) {
	return readln.split.to!T;
}

T[][] readMatrix(T)(uint height, uint width) if (!isSomeChar!T) {
	auto res = new T[][](height, width);
	foreach(i; 0..height) {
		res[i] = readAs!(T[]);
	}
	return res;
}

T[][] readMatrix(T)(uint height, uint width) if (isSomeChar!T) {
	auto res = new T[][](height, width);
	foreach(i; 0..height) {
		auto s = rs;
		foreach(j; 0..width) res[i][j] = s[j].to!T;
	}
	return res;
}

int ri() {
	return readAs!int;
}

double rd() {
	return readAs!double;
}

string rs() {
	return readln.chomp;
}
