#pragma region // https://oj.uz/problem/view/IOI08_printer
#include<bits/stdc++.h>
#define int long long
#pragma GCC optimize("Ofast,unroll-loops,no-stack-protector,fast-math")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma comment(linker, "/stack:200000000")
#define f2(i, m) for(int i=0; i<m; i++)
#define f21(i, m) for(int i=1; i<m; i++)
#define f3(i, n, m) for(int i=n; i<m; i++)
#define f2_(i, m) for(int i=m; i>-1; i--)
#define f21_(i, m) for(int i=m; i>0; i--)
#define f3_(i, n, m) for(int i=n; i>=m; i--)
#define travG(idx) for(int i : g[idx])
#define travG_(i, idx) for(int i : g[idx])
#define trav(loop) for(int i : loop)
#define trav_(i, loop) for(int i : loop)
#define trav2(loop, idx) for(int i : loop[idx])
#define trav2_(i, loop, idx) for(int i : loop[idx])
#define ll long long
#define bs bitset
#define pii pair<int, int>
#define vi vector<int>
#define vvi vector<vector<int>>
#define ve vector<element>
#define ve_ vector<element_>
#define vpii vector<pair<int, int>>
#define dqi deque<int>
#define dqpii deque<pii>
#define qi queue<int>
#define qe queue<element>
#define qpii queue<pair<int, int>>
#define si stack<int>
#define se stack<element>
#define spii stack<pair<int, int>>
#define vb vector<bool>
#define pqi priority_queue<int>
#define pqi_ priority_queue<int, vi, greater<int>>
#define pqpii priority_queue<pair<int, int>>
#define pqpii_ priority_queue<pair<int, int>, vpii, greater<pii>>
#define pb push_back
#define pf push_front
#define pob pop_back()
#define pof pop_front()
#define len length()
#define elif else if
#define mod 1000000007
#pragma endregion
//#define debug
/*
#ifdef debug
#endif
#ifndef debug
#endif
*/
using namespace std;
constexpr int mxn=3e4+1, mxq=3e4+1;
constexpr bool debug = 0;
int n, m, srt, stp;
set<int> e[mxn];
void bfs()
{
struct node
{
int u, v, dis;
node(int u, int v, int d) : u(u), v(v), dis(d) {}
};
unordered_map<int, int> dis[mxn];
deque<node> dq;
bitset<mxn> vis;
for(int i : e[srt])
{
dq.pb(node(srt, i, 0));
}
vis[srt] = 1;
while(!dq.empty())
{
node cur = dq.front(); dq.pof;
if(debug)
{
cout<<cur.u<<' '<<cur.v<<' '<<cur.dis<<'\n';
}
if(cur.u == stp)
{
cout << cur.dis;
return;
}
if(!vis[cur.u])
{
for(int i : e[cur.u])
{
if(dis[cur.u][i]==0 || cur.dis<dis[cur.u][i])
{
vis[cur.u] = 1;
dis[cur.u][i] = cur.dis;
dq.pf(node(cur.u, i, cur.dis));
}
}
}
f2(i, 2)
{
int nxt=i?+cur.v:-cur.v; nxt+=cur.u;
if(nxt>=0 && nxt<n && (dis[nxt][cur.v]==0 || cur.dis+1<dis[nxt][cur.v]))
{
dis[nxt][cur.v] = cur.dis+1;
dq.pb(node(nxt, cur.v, cur.dis+1));
}
}
}
cout << -1;
}
signed main()// https://oj.uz/problem/view/APIO16_boat
{ ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
//input
{
cin >> n >> m;
f2(i, m)
{
int u, v; cin>>u>>v;
e[u].insert(v);
i<2 && ((i?stp:srt) = u);
}
}
bfs();
return 0;
}
