#include <bits/stdc++.h>
using namespace std;
const int INF = 2000000000;
const long long LINF = 9000000000000000000;
const long double EPS = 0.00001;
bool AinB(long long a, long long b, long long c, long long d) {
  return c <= a && a <= d && c <= b && b <= d;
}
bool isller(long long a, long long b, long long c, long long d) {
  return (a <= c && c <= b) || (a <= d && d <= b) || (c <= a && a <= d) ||
         (c <= b && b <= d);
}
template <class T, class F, T fZero>
struct Node {
  F f;
  Node<T, F, fZero> *L, *R;
  T t;
  void recalc() {
    t = f((L != nullptr ? L->t : fZero), (R != nullptr ? R->t : fZero));
  }
  Node(Node<T, F, fZero> *Left, Node<T, F, fZero> *Right) {
    L = Left;
    R = Right;
    recalc();
  }
};
template <class T, class F, T fZero>
T get(Node<T, F, fZero> *v, long long tl, long long tr, long long l,
      long long r) {
  if (AinB(tl, tr, l, r)) {
    return v->t;
  } else if (!isller(tl, tr, l, r)) {
    return fZero;
  } else {
    long long tm = (tl + tr) / 2;
    return v->f(get(v->L, tl, tm, l, r), get(v->R, tm + 1, tr, l, r));
  }
}
template <class T, class F, T fZero>
void update(Node<T, F, fZero> *v, long long tl, long long tr, long long pos,
            T val) {
  if (tl == pos && tl == tr) {
    v->t = val;
  } else {
    long long tm = (tl + tr) / 2;
    if (pos <= tm) {
      update(v->L, tl, tm, pos, val);
    } else {
      update(v->R, tm + 1, tr, pos, val);
    }
    v->recalc();
  }
}
template <class T, class F, T fZero>
void build(Node<T, F, fZero> *&v, long long tl, long long tr, vector<T> &a) {
  if (tl == tr) {
    v->t = a[tl];
  } else {
    long long tm = (tl + tr) / 2;
    Node<T, F, fZero> *Left = new Node<T, F, fZero>(nullptr, nullptr);
    Node<T, F, fZero> *Right = new Node<T, F, fZero>(nullptr, nullptr);
    build(Left, tl, tm, a);
    build(Right, tm + 1, tr, a);
    v->L = Left;
    v->R = Right;
    v->recalc();
  }
}
struct Min {
  long long operator()(long long a, long long b) { return (a < b ? a : b); }
};
struct Sum {
  long long operator()(long long a, long long b) { return a + b; }
};
void solve() {
  int c, v0, v1, a, l;
  cin >> c >> v0 >> v1 >> a >> l;
  int pos = 0;
  int v = v0;
  int day = 0;
  while (pos < c) {
    if (day != 0) v += a;
    if (v > v1) v = v1;
    pos += v - min(l, pos);
    ++day;
  }
  cout << day;
  return;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  cout.precision(20);
  solve();
  return 0;
}
