"""経路数を数える。小数で数えればよい。"""
import numpy as np

MOD = 10**9 + 7

N, M, T, *G = map(int, open(0).read().split())
A = np.zeros((N, N))
for frm, to in zip(G[::2], G[1::2]):
    A[frm,to] += 1

B = np.linalg.matrix_power(A, T)
ans = np.sum(B[0] != 0)
if ans == 0:
    ans = -1
print(ans)