//Don't have to see. start------------------------------------------
var read = require('readline').createInterface({
	input: process.stdin, output: process.stdout
});
var obj; var inLine = []; var outputList = [];var retcode = new Set();
read.on('line', function(input){
	var tmp = input.split(' ');
	for(var i = 0; i < tmp.length; i++){
		inLine.push(tmp[i]);
		if(i == tmp.length - 1){
			retcode.add(inLine.length);
		}
	}
});
read.on('close', function(){
	obj = init(inLine);
	console.error('\n↑入力 ↓出力');
	Main();
	console.log(myconv(outputList, 9));
});
function makeClone(obj){return (obj instanceof Set) ? new Set(Array.from(obj)) : JSON.parse(JSON.stringify(obj));}
function nextArray(size, code){
	var ret = new Array(size);
	for(var i = 0; i < size; i++){
		if(code == 'int'){
			ret[i] = nextInt();
		}else if(code == 'long'){
			ret[i] = BigInt(next());
		}else{
			ret[i] = next();
		}
	}
	return ret;
}
function nextIntArray(size){return nextArray(size, 'int');} function nextStrArray(size){return nextArray(size, 'str');} function nextLongArray(size){return nextArray(size, 'long');}
function nextCharArray(){return myconv(next(),6);}
function next(){return obj.next();} function hasNext(){return obj.hasNext();} function nextInt(){return myconv(next(),1);} function nextLong(){return BigInt(next());}
function getCountMap(list){
	var map = {};
	for(var i = 0; i < list.length; i++){
		if(map[list[i]] == null){
			map[list[i]] = 0;
		}
		map[list[i]]++;
	}
	return map;
}
function init(input){  
	return {
		list : input, index : 0, max : input.length,
		hasNext : function(){return (this.index < this.max);},
		next : function(){if(this.hasNext()){return this.list[this.index++];}else{throw 'ArrayIndexOutOfBoundsException ‚There is no more input';}},
		isReturn : function(){return retcode.has(this.index);}
	};
}
function myout(s){outputList.push(s);}
function myerr(s){console.error('debug:' + require('util').inspect(s,false,null));}
function isReturn(){return obj.isReturn();}
//param "no" is
//unknown or outlier : return i. 1: parseInt.
//2: split space. 4: split space and parseInt.
//6: split 1 character. 7: split 1 character and parseInt.
//8: join space. 9: join nextline. 0: join no character.
function myconv(i,no){try{switch(no){case 1:return parseInt(i);case 2:return i.split(' ');case 4:return i.split(' ').map(Number);case 6:return i.split('');case 7:return i.split('').map(Number);case 8:return i.join(' ');case 9:return i.join('\n');case 0:return i.join('');default:return i;}}catch(e){return i;}}

//Don't have to see. end------------------------------------------
function Main(){
	var N = nextInt();
	var M = nextInt();
	var list = new Array(N);
	for(var i = 0; i < N; i++){
		list[i] = {
			child : [],
			count : -1
		};
	}
	for(var i = 0; i < M; i++){
		var L = nextInt() - 1;
		var R = nextInt() - 1;
		list[L].child.push(R);
		list[R].child.push(L);
	}
	var queue = new ArrayDeque();
	queue.add(0);
	list[0].count = 0;
	while(queue.size() > 0){
		var now = queue.pollFirst();
		var child = list[now].child;
		for(var i = 0; i < child.length; i++){
			var c = child[i];
			if(list[c].count == -1){
				list[c].count = list[now].count + 1;
				queue.addLast(c);
			}
		}
	}
	myout(list[N - 1].count);
}
function ArrayDeque(add){
	var queue = {
		L : 0,//next add Area
		R : 0,//next add Area
		map : {},
		unshift : function(V){ return this.addFirst(V); },
		addFirst : function(V){
			this.map[this.L] = V;
			if(this.L == this.R){
				this.R++;
			}
			this.L--;
		},
		shift : function(){ return this.pollFirst(); },
		pollFirst : function(){
			if(this.L == this.R){
				return null;
			}
			var ret = this.map[this.L + 1];
			this.L++;
			if(Math.abs(this.L - this.R) == 1){
				this.R--;
			}
			return ret;
		},
		peekFirst : function(){
			if(this.L == this.R){
				return null;
			}
			return this.map[this.L + 1];
		},
		add : function(V){ return this.addLast(V); },
		push : function(V){ return this.addLast(V); },
		addLast : function(V){
			this.map[this.R] = V;
			if(this.L == this.R){
				this.L--;
			}
			this.R++;
		},
		pop : function(){ return this.pollLast(); },
		pollLast : function(){
			if(this.L == this.R){
				return null;
			}
			var ret = this.map[this.R - 1];
			this.R--;
			if(Math.abs(this.L - this.R) == 1){
				this.L++;
			}
			return ret;
		},
		peekLast : function(){
			if(this.L == this.R){
				return null;
			}
			return this.map[this.R - 1];
		},
		size : function(){
			if(this.L == this.R){
				return 0;
			}else{
				return Math.abs(this.L - this.R) - 1;
			}
		},
		toString : function(){
			var list = [];
			for(var i = this.L + 1; i < this.R; i++){
				list.push(this.map[i]);
			}
			return "[" + list.join(", ") + "]";
		},
		get : function(index){
			if(this.L + 1 + index >= this.R || index < 0){
				return null;
			}else{
				return this.map[this.L + 1 + index];
			}
		},
		set : function(index, V){
			if(this.L + 1 + index >= this.R || index < 0){
				throw 'ArrayIndexOutOfBoundsException can\'t set';
			}else{
				this.map[this.L + 1 + index] = V;
			}
		},
		isEmpty : function(){
			return this.size() == 0;
		},
		clear : function(){
			this.L = 0;
			this.R = 0;
			this.map = {}
		}
	}
	if(add){
		for(var i = 0; i < add.length; i++){
			queue.addLast(add[i]);
		}
	}
	return queue;
}