#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;
using lint = long long;
using ulint = unsigned long long;
using llint = __int128_t;
#define endl '\n'
int const INF = 1<<30;
lint const INF64 = 1LL<<61;
lint const mod107 = 1e9+7;
using mint107 = modint1000000007;
long const mod = 998244353;
using mint = modint998244353;
lint ceilDiv(lint x, lint y){if(x >= 0){return (x+y-1)/y;}else{return x/y;}}
lint floorDiv(lint x, lint y){if(x >= 0){return x/y;}else{return (x-y+1)/y;}}
lint Sqrt(lint x) {assert(x >= 0); lint ans = sqrt(x); while(ans*ans > x)ans--; while((ans+1)*(ans+1)<=x)ans++; return ans;}
lint gcd(lint a,lint b){if(a<b)swap(a,b);if(a%b==0)return b;else return gcd(b,a%b);}
lint lcm(lint a,lint b){return (a / gcd(a,b)) * b;}
lint chmin(vector<lint>&v){lint ans = INF64;for(lint i:v){ans = min(ans, i);}return ans;}
lint chmax(vector<lint>&v){lint ans = -INF64;for(lint i:v){ans = max(ans, i);}return ans;}
double dist(double x1, double y1, double x2, double y2){return sqrt(pow(x1-x2, 2) + pow(y1-y2,2));}
string toString(lint n){string ans = "";if(n == 0){ans += "0";}else{while(n > 0){int a = n%10;char b = '0' + a;string c = "";c += b;n /= 10;ans = c + ans;}}return ans;}
string toString(lint n, lint k){string ans = toString(n);string tmp = "";while(ans.length() + tmp.length() < k){tmp += "0";}return tmp + ans;}
vector<lint>prime;void makePrime(lint n){prime.push_back(2);for(lint i=3;i<=n;i+=2){bool chk = true;for(lint j=0;j<prime.size() && prime[j]*prime[j] <= i;j++){if(i % prime[j]==0){chk=false;break;}}if(chk)prime.push_back(i);}}
lint Kai[20000001]; bool firstCallnCr = true; 
lint ncrmodp(lint n,lint r,lint p){ if(firstCallnCr){ Kai[0] = 1; for(int i=1;i<=20000000;i++){ Kai[i] = Kai[i-1] * i; Kai[i] %= p;} firstCallnCr = false;} if(n<0)return 0;
if(n < r)return 0;if(n==0)return 1;lint ans = Kai[n];lint tmp = (Kai[r] * Kai[n-r]) % p;for(lint i=1;i<=p-2;i*=2){if(i & p-2){ans *= tmp;ans %= p;}tmp *= tmp;tmp %= p;}return ans;}
#define rep(i, n) for(int i = 0; i < n; i++)
#define repp(i, x, y) for(int i = x; i < y; i++)
#define vec vector
#define pb push_back
#define se second
#define fi first
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
unsigned long Rand() {
  static unsigned long x=123456789, y=362436069, z=521288629, w=88675123;
  unsigned long t=(x^(x<<11));
  x=y; y=z; z=w;
  return ( w=(w^(w>>19))^(t^(t>>8)) );
}
struct Point {
    lint x, y;
    int quad;
    Point(lint X, lint Y) {
        x = X;
        y = Y;
        quad = getQuadrant();
    }
    int getQuadrant() {
        if(x >= 0) {
            if(y >= 0) return 1;
            else return 4;
        } else {
            if(y >= 0) return 2;
            else return 3;
        }
    }
};

bool operator<(const Point &left, const Point &right) {
    if(left.quad == right.quad) {
        return left.y * right.x < left.x * right.y;
    } else {
        return left.quad < right.quad;
    }
}

struct Frac {
    lint upper, lower;
    Frac() {
        Frac(0,1);
    }
    Frac(lint u, lint l) {
        assert(l != 0);
        if(u <= 0 && l < 0) {
            upper = -u;
            lower = -l;
        } else {
            upper = u;
            lower = l;
        }
        reduction();
    }

    Frac(lint u) {
        upper = u;
        lower = 1;
    } 

    void reduction() {
        if(upper != 0) {
            lint g = gcd(abs(upper), abs(lower));
            upper /= g;
            lower /= g;
        
            if(lower < 0) {
                lower *= -1;
                upper *= -1;
            }
        } else {
            lower = 1;
        }
    }

    Frac operator+(const Frac &other) {
        lint L = lower * other.lower;
        lint U = upper*other.lower + lower*other.upper;
        return Frac(U, L);
    }

    Frac operator-(const Frac &other) {
        lint L = lower * other.lower;
        lint U = upper*other.lower - lower*other.upper;
        upper = U;
        lower = L;
        return Frac(U, L);
    }

    bool operator<=(const Frac &other) {
        return upper*other.lower <= lower*other.upper;
    }

    Frac operator*(const Frac &other) {
        lint L = lower * other.lower;
        lint U = upper * other.upper;
        return Frac(U, L);
    }

    Frac operator/(const Frac &other) {
        assert(other.upper != 0);
        lint L = lower * other.upper;
        lint U = upper * other.lower;
        return Frac(U, L);
    }
};

bool operator<(const Frac &left, const Frac &right) {
    return left.upper*right.lower < left.lower*right.upper;
}
lint extGCD(lint a, lint b, lint &x, lint &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    lint d = extGCD(b, a%b, y, x);
    y -= a/b * x;
    return d;
}
struct edge{
    int to;
};
using graph = vector<vector<edge>>;

lint n,m;
graph g(100000);

void f(int start, vec<lint>&dist) {
    dist[start] = 0;
    priority_queue<vec<lint>>que;
    que.push({0, start});
    while(!que.empty()) {
        auto q = que.top();
        que.pop();
        lint v = q[1];
        for(auto e: g[v]) {
            if(dist[e.to] > dist[v] + 1) {
                que.push({e.to, v});
            }
        }
    }
}

int main(){
    cin >> n >> m;
    int u[m], v[m];
    vec<vec<lint>>dist(3, vec<lint>(n, INF64));
    rep(i, m) {
        cin >> u[i] >> v[i];
        u[i]--;v[i]--;
        g[u[i]].pb({v[i]});
    }
    f(0, dist[0]);
    f(n-1, dist[1]);
    f(n-2, dist[2]);

    lint ans = min(dist[0][n-1] + dist[1][n-2] + dist[2][0], dist[0][n-2] + dist[2][n-1] + dist[1][0]);
    cout << ans << endl;

    
    
}