"""数え上げ mod 2^{64} をとる「嘘解法」。
これはたぶん落ちると思う。"""

import sys
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

MOD = 10**9 + 7

def mult(A, B):
    """行列積 mod 2^64"""
    return np.dot(A, B)

def mat_pow(A, n):
    if n == 0:
        return np.eye(len(A), dtype=np.int64)
    X = mat_pow(A, n // 2)
    X = mult(X, X)
    return mult(A, X) if n & 1 else X

N, M, T = map(int, readline().split())
A = np.zeros((N, N), np.int64)
m = map(int, read().split())
for frm, to in zip(m, m):
    A[to, frm] += 1

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