import java.util.*;
import java.util.regex.*;
import java.lang.*;
import java.io.*;
 
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		String str = "1=0;1;123.456;4;5;6;5;\n 2=1;2;451.467;6;7;8;6;\n 3=2;3;765.654;8;3;2;4;\n 4=1;2;451.467;6;7;8;6;";
		Pattern pattern = Pattern.compile("(?m)^1=(.*)");
		Matcher m = pattern.matcher(str);
		if (m.find()) {
			System.out.println("Найдено: " + m.group(1));
		}
		else {
			System.out.println("Не найдено");
		};
	}
}

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