# 嘘解法

N, M, T, *nums = map(int, open(0).read().split())
G = set(zip(nums[::2], nums[1::2]))

T_max = min(N*N+10*N, T)
T0 = [-1] * N
T1 = [-1] * N
dp = [0] * N
dp[0] = 1
for t in range(T_max):
    newdp = [0] * N
    for frm, to in G:
        if dp[frm] and not newdp[to]:
            newdp[to] = 1
            T0[to], T1[to] = T1[to], t
    dp = newdp

ans = 0
for v in range(N):
    if T == T_max:
        ans += dp[v]
    else:
        t0, t1 = T0[v], T1[v]
        if t0 == -1:
            continue
        ans += (T-t1) % (t1-t0) == 0
if ans == 0:
    ans = -1
print(ans)