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#ifndef LOCAL
#pragma GCC optimize ("O3")
#endif

#include <bits/stdc++.h>

using namespace std;

#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return {i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (c it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(x...) " [" #x ": " << (x) << "] "

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
template <typename A, typename B>
using unordered_map2 = __gnu_pbds::gp_hash_table<A, B>;
using namespace __gnu_pbds;
template <typename T> using ordered_set =
  __gnu_pbds::tree<T, __gnu_pbds::null_type, less<T>, __gnu_pbds::rb_tree_tag,
                   __gnu_pbds::tree_order_statistics_node_update>;
// ordered_set<int> s; s.insert(1); s.insert(2);
// s.order_of_key(1);    // Out: 0.
// *s.find_by_order(1);  // Out: 2.

using ld = long double;
using ll = long long;

constexpr int mod = 1000 * 1000 * 1000 + 7;
constexpr int odw2 = (mod + 1) / 2;

void OdejmijOd(int& a, int b) { a -= b; if (a < 0) a += mod; }
int Odejmij(int a, int b) { OdejmijOd(a, b); return a; }
void DodajDo(int& a, int b) { a += b; if (a >= mod) a -= mod; }
int Dodaj(int a, int b) { DodajDo(a, b); return a; }
int Mnoz(int a, int b) { return (ll) a * b % mod; }
void MnozDo(int& a, int b) { a = Mnoz(a, b); }
int Pot(int a, ll b) { int res = 1; while (b) { if (b % 2 == 1) MnozDo(res, a); a = Mnoz(a, a); b /= 2; } return res; }
int Odw(int a) { return Pot(a, mod - 2); }
void PodzielDo(int& a, int b) { MnozDo(a, Odw(b)); }
int Podziel(int a, int b) { return Mnoz(a, Odw(b)); }
int Moduluj(ll x) { x %= mod; if (x < 0) x += mod; return x; }

template <typename T> T Maxi(T& a, T b) { return a = max(a, b); }
template <typename T> T Mini(T& a, T b) { return a = min(a, b); }

struct Data {
  vector<int> graf;
  bool wylaczony;
  int dp;

  Data() : graf(), wylaczony(false), dp(0) {}
};

int n, m, k;
vector<Data> node;

vector<int> ZnajdzSciezke(int len) {
  vector<int> res;
  assert(1 <= len);
  for (int i = n - 1; i >= 0; i--) {
    Data& d = node[i];
    d.dp = 0;
    if (d.wylaczony) continue;
    d.dp = 1;
    for (int x : d.graf) {
      Maxi(d.dp, node[x].dp + 1);
    }
    if (d.dp == len) {
      res.push_back(i);
      while ((int) res.size() < len) {
        i = res.back();
        Data& dat = node[i];
        for (int x : dat.graf) {
          if (node[x].dp + 1 == dat.dp) {
            res.push_back(x);
            break;
          }
        }
        assert(i != res.back());
      }
      return res;
    }
  }
  return res;
}

bool Generuj(int len, int zostalo) {
  vector<int> sciezka = ZnajdzSciezke(len);
  debug() << "Generuj(" imie(len) imie(zostalo) ")" imie(sciezka);
  if (sciezka.empty()) return true;
  if (zostalo == 0) return false;
  for (int x : sciezka) {
    assert(!node[x].wylaczony);
    node[x].wylaczony = true;
    debug() << imie(x);
    if (Generuj(len, zostalo - 1)) {
      return true;
    }
    node[x].wylaczony = false;
  }
  return false;
}

bool Zabijam(int len) {
  for (int i = 0; i < n; i++) {
    node[i].wylaczony = false;
  }
  const bool result = Generuj(len, k);
  debug() << "Zabijam(" imie(k) imie(len) ")" imie(result);
  return result;
}

int LiczDp() {
  int naj = 0;
  for (int i = n - 1; i >= 0; i--) {
    Data& d = node[i];
    d.dp = 0;
    if (d.wylaczony) continue;
    d.dp = 1;
    for (int x : d.graf) {
      Maxi(d.dp, node[x].dp + 1);
    }
    Maxi(naj, d.dp);
  }
  return naj;
}

int Potega(int x, int p) {
  assert(0 <= x and 0 <= p);
  int res = 1;
  while (p--) res *= x;
  return res;
}

pair<int, int> BinSearch(int a_, int b_) {
  auto BinSearch_ = [](int a, int b) -> pair<int, int> {
    if (a == b) {
      return {0, -1};
    }
    pair<int, int> res = {numeric_limits<int>::max(), -1};
    for (int c = a; c < b; c++) {
      const int koszt = max(BinSearch(a, c).first, BinSearch(c + 1, b).first)
          + Potega(c, k);
      if (koszt < res.first) {
        res = {koszt, c};
      }
    }
    assert(a <= res.second and res.second < b);
    return res;
  };
  static map<pair<int, int>, pair<int, int>> memo;
  auto it = memo.find(make_pair(a_, b_));
  if (it != memo.end()) {
    return it->second;
  }
  return memo[make_pair(a_, b_)] = BinSearch_(a_, b_);
}

int brut_wynik = numeric_limits<int>::max();

void Baktracz(int pos, int zostalo, int mam) {
  if (pos == -1) {
    Mini(brut_wynik, mam);
    return;
  }
  node[pos].dp = 1;
  for (int x : node[pos].graf) {
    Maxi(node[pos].dp, node[x].dp + 1);
  }
  Baktracz(pos - 1, zostalo, max(mam, node[pos].dp));
  if (zostalo > 0) {
    node[pos].dp = 0;
    Baktracz(pos - 1, zostalo - 1, mam);
  }
}

int Brut() {
  Baktracz(n - 1, k, 0);
  cout << brut_wynik << endl;
  return 0;
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> m >> k;
  node.resize(n);
  while (m--) {
    int a, b;
    cin >> a >> b;
    a--; b--;
    assert(0 <= a and a < b and b < n);
    node[a].graf.push_back(b);
  }
  if (n <= 50) {
    return Brut();
  }
  int a = 1, b = LiczDp() + 1;
  while (a < b) {
    const int c = BinSearch(a, b).second;
    debug() << imie(a) imie(b) imie(c);
    if (Zabijam(c)) {
      b = c;
    } else {
      a = c + 1;
    }
  }
  cout << a - 1 << endl;
  return 0;
}