#include <cstdio>
#define rep(i, d, u) for(int i = d; i <= u; ++i)
#define gep(i, a) for(int i = firs[a]; i; i = neig[i])
int ured() {
	int ch, re = 0;
	do {
		ch = getchar();
	} while(ch < '0' || '9' < ch);
	do {
		re = re * 10 + (ch ^ '0');
	} while('0' <= (ch = getchar()) && ch <= '9');
	return re;
}
void uwit(int da) {
	int ch[21], cn = 0;
	do {
		ch[++cn] = da % 10;
	} while(da /= 10);
	do {
		putchar('0' ^ ch[cn]);
	} while(--cn);
}
const int _maxn = 100011, _maxm = 100011;
int n, m, u, v, firs[_maxn], neig[_maxm << 1], arri[_maxm << 1], queu[_maxn], dist[_maxn], head, tail;
int main() {
	n = ured(), m = ured();
	rep(i, 1, m) {
		u = ured(), v = ured(), neig[i << 1] = firs[u], firs[u] = i << 1, arri[i << 1] = v;
		neig[i << 1 | 1] = firs[v], firs[v] = i << 1 | 1, arri[i << 1 | 1] = u;
	}
	dist[queu[++tail] = 1] = 1;
	while(head < tail) {
		gep(i, queu[++head]) {
			if(!dist[arri[i]]) {
				dist[queu[++tail] = arri[i]] = dist[queu[head]] + 1;
			}
		}
	}
	uwit(dist[n] - 2), putchar('\n');
	return 0;
}