"""bit並列化"""
import sys

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

def mult(A, B):
    N = len(A)
    C = [0] * N
    # A[i,j] == 1 のとき、 C[i,:] |= B[j,:] となるので
    for i in range(N):
        for j in range(N):
            if A[i] & (1 << j):
                C[i] |= B[j]
    return C

def mat_pow(A, n):
    N = len(A)
    if n == 0:
        return [1 << n for n in range(N)]
    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 = [0] * N
m = map(int, read().split())
for frm, to in zip(m, m):
    A[frm] |= 1 << to

B = mat_pow(A, T)
ans = bin(B[0]).count('1')
if ans == 0:
    ans = -1
print(ans)