import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); }
void log()(){ writeln(""); } void log(T, A ...)(T t, lazy A a){ if(DEBUG) write(t, " "), log(a); } bool DEBUG = 0; 
string read(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
T rtype(T)(){ return read.to!T; } alias rint = rtype!int, rlong = rtype!long, rreal = rtype!real;
T[] rtypes(T)(int n){ return n.iota.map!(i => rtype!T()).array; } alias rint = rtypes!int, rlong = rtypes!long, rreal = rtype!real;

// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //

void solve(){
	int n = rint;
	
	int[][] af;
	foreach(i; 0 .. n) af ~= rint(n - 1).map!(x => x - 1).array;
	log("af:", af);
	
	int[] js = new int[](n);
	int cnt;
	int[] isDone = new int[](n);
	while(1){
		int f = 0;
		foreach(i; 0 .. n) isDone[i] = 0;
		foreach(i; 0 .. n){
			if(js[i] >= n - 1) continue;
			if(isDone[i]) continue;
			if(f == 0) f = 1;
			int x = af[i][js[i]];
			if(! isDone[x] && af[x][js[x]] == i){
				js[i] += 1;
				js[x] += 1;
				f = 2;
				isDone[i] = 1, isDone[x] = 1;
			}
			log("cnt:", cnt, "i:", i, "f:", f, "js:", js);
		}
		if(f == 0) break;
		if(f == 1){
			"-1".writeln;
			return;
		}
		cnt += 1;
	}
	
	cnt.writeln;
}
