(n, m, t) = map(int,input().split())

#行列の積
def mul(a, b):
    c = [[0 for j in range(n)] for i in range(n)]
    for i in range(n):
        for j in range(n):
            for k in range(n):
                c[i][j] |= a[i][k] & b[k][j]
    return c

#有向グラフを行列に置き換える
G = [[0 for j in range(n)] for i in range(n)]

for i in range(m):
    (a, b) = map(int,input().split())
    G[b][a] = 1

# A = G ** T
A = [[0 for j in range(n)] for i in range(n)]

for i in range(n):
    A[i][i] = 1

while t:
    if t % 2 == 1:
        A = mul(A, G)
    G = mul(G, G)
    t = t // 2

#answer
ans = 0
for i in range(n):
    ans += A[i][0]

if ans == 0:
    print(-1)
else:
    print(ans)