#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9 + 7;
template <class T>
void dbs(string str, T t) {
  cout << str << " : " << t << endl;
}
template <class T, class... second>
void dbs(string str, T t, second... s) {
  int idx = str.find(',');
  cout << str.substr(0, idx) << " : " << t << ",";
  dbs(str.substr(idx + 1), s...);
}
template <class second, class T>
ostream& operator<<(ostream& os, const pair<second, T>& p) {
  return os << "(" << p.first << ", " << p.second << ")";
}
template <class T>
ostream& operator<<(ostream& os, const vector<T>& p) {
  os << "[ ";
  for (auto& it : p) os << it << " ";
  return os << "]";
}
template <class T>
ostream& operator<<(ostream& os, const set<T>& p) {
  os << "[ ";
  for (auto& it : p) os << it << " ";
  return os << "]";
}
template <class second, class T>
ostream& operator<<(ostream& os, const map<second, T>& p) {
  os << "[ ";
  for (auto& it : p) os << it << " ";
  return os << "]";
}
template <class T>
void prc(T a, T b) {
  cout << "[";
  for (T i = a; i != b; ++i) {
    if (i != a) cout << ", ";
    cout << *i;
  }
  cout << "]";
  cout << endl;
}
int main() {
  int x, h, m;
  cin >> x >> h >> m;
  int y = 0;
  while (1) {
    if (h % 10 == 7 || h / 10 == 7 || m % 10 == 7 || m / 10 == 7) break;
    m -= x;
    if (m < 0) {
      h--;
      m += 60;
      if (h < 0) h += 24;
    }
    y++;
  }
  cout << y << "\n";
}
