#include <stdio.h>  
#include <string.h>  
#include <queue>  
#include <vector>  
using namespace std;  
struct node  
{  
    int end;  
    int dis;  
    bool friend operator <(node a,node b)  
    {  
        return a.dis > b.dis;  
    }  
};  
const int MAX = 10010;  
int n,m;  
int dis[MAX];  
int degree[MAX];  
vector <int> v[MAX];  
void dijkstra()  
{  
    int i;  
    for(i = 1;i <= n; i++)  
        dis[i] = 0x7fffffff;  
    dis[1] = 0;  
    node t;  
    t.end = 1;  
    t.dis = 0;  
    priority_queue <node> q;  
    q.push(t);  
    while(!q.empty())  
    {  
        t = q.top();  
        q.pop();  
        int len = v[t.end].size();  
        for(i = 0;i < len; i++)  
        {  
            node tt;  
            int k = v[t.end][i];  
            if(dis[k] > t.dis + v[t.end].size() - 1)  
            {  
                dis[k] = t.dis + v[t.end].size() - 1;  
                tt.end = k;  
                tt.dis = dis[k];  
                q.push(tt);  
            }  
        }  
    }  
}  
int main()  
{  
    node x;  
    int s,e,i;  
    while(scanf("%d %d",&n,&m)!=EOF)  
    {  
        //memset(degree,0,sizeof())  
        for(i = 1;i <= n; i++)  
            v[i].clear();  
        while(m--)  
        {  
            scanf("%d %d",&s,&e);  
            v[s].push_back(e);  
        }  
        dijkstra();  
        if(dis[n] == 0x7fffffff)  
            puts("-1");  
        else  
            printf("%d\n",dis[n]);  
    }  
    return 0;  
}