#include <bits/stdc++.h>
using namespace std;
template <class T>
inline T bigmod(T p, T e, T M) {
  long long ret = 1;
  for (; e > 0; e >>= 1) {
    if (e & 1) ret = (ret * p) % M;
    p = (p * p) % M;
  }
  return (T)ret;
}
template <class T>
inline T gcd(T a, T b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
template <class T>
inline T modinverse(T a, T M) {
  return bigmod(a, M - 2, M);
}
template <class T>
inline T lcm(T a, T b) {
  a = abs(a);
  b = abs(b);
  return (a / gcd(a, b)) * b;
}
template <class T, class X>
inline bool getbit(T a, X i) {
  T t = 1;
  return ((a & (t << i)) > 0);
}
template <class T, class X>
inline T setbit(T a, X i) {
  T t = 1;
  return (a | (t << i));
}
template <class T, class X>
inline T resetbit(T a, X i) {
  T t = 1;
  return (a & (~(t << i)));
}
inline long long power(long long a, long long b) {
  long long multiply = 1;
  for (int i = (0); i < (b); i++) {
    multiply *= a;
  }
  return multiply;
}
bool comp(pair<int, int> x, pair<int, int> y) { return x.second < y.second; }
bool intersect(pair<int, int> a, pair<int, int> b) {
  vector<pair<int, int> > temp;
  temp.push_back(a);
  temp.push_back(b);
  sort(temp.begin(), temp.end(), comp);
  if (temp[1].first < temp[0].second) return true;
  return false;
}
int main() {
  int a, ta, b, tb, h, m;
  vector<pair<int, int> > all;
  cin >> a >> ta >> b >> tb;
  scanf("%d:%d", &h, &m);
  int start = 5 * 60;
  for (int i = start; i <= 23 * 60 + 59; i += b) {
    all.push_back(make_pair(i, i + tb));
  }
  int s = h * 60 + m;
  int e = s + ta;
  int cnt = 0;
  for (int i = (0); i < (all.size()); i++) {
    if (intersect(make_pair(s, e), all[i])) cnt++;
  }
  cout << cnt << "\n";
  return 0;
}
