#include <iostream>
#include <string>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <utility>
using namespace std;
int dp[100001];
int M, N;
typedef pair<int, int> PAIR;
bool cmp(PAIR x, PAIR y) {
if (x.first < y.first){
return true;
}
else if (x.first == y.first) {
return x.second < y.second;
}
else {
return false;
}
}
int main(void) {
int x, y;
vector<PAIR> edge;
cin >> N >> M;
for (int i = 0; i < M; i++) {
cin >> x >> y;
edge.push_back(PAIR(x, y));
}
sort(edge.begin(), edge.end());
for (vector<PAIR>::iterator itor = edge.begin(); itor != edge.end(); itor++) {
x = itor->first; y = itor->second;
if (x != 1 && dp[x] == 0) continue;
if (dp[y] == 0 || dp[y] > dp[x] + 1) {
dp[y] = dp[x] + 1;
}
}
if (dp[N] == 0) cout << -1 << endl;
else cout << dp[N] << endl;
return 0;
}
