#include <bits/stdc++.h>
using namespace std;
const int MOD = (int)1e9 + 7;
const int FFTMOD = 119 << 23 | 1;
const int INF = (int)1e9 + 23111992;
const long long LINF = (long long)1e18 + 23111992;
const long double PI = acos((long double)-1);
const long double EPS = 1e-9;
inline long long gcd(long long a, long long b) {
  long long r;
  while (b) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
inline long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
inline long long fpow(long long n, long long k, int p = MOD) {
  long long r = 1;
  for (; k; k >>= 1) {
    if (k & 1) r = r * n % p;
    n = n * n % p;
  }
  return r;
}
template <class T>
inline int chkmin(T& a, const T& val) {
  return val < a ? a = val, 1 : 0;
}
template <class T>
inline int chkmax(T& a, const T& val) {
  return a < val ? a = val, 1 : 0;
}
inline unsigned long long isqrt(unsigned long long k) {
  unsigned long long r = sqrt(k) + 1;
  while (r * r > k) r--;
  return r;
}
inline long long icbrt(long long k) {
  long long r = cbrt(k) + 1;
  while (r * r * r > k) r--;
  return r;
}
inline void addmod(int& a, int val, int p = MOD) {
  if ((a = (a + val)) >= p) a -= p;
}
inline void submod(int& a, int val, int p = MOD) {
  if ((a = (a - val)) < 0) a += p;
}
inline int mult(int a, int b, int p = MOD) { return (long long)a * b % p; }
inline int inv(int a, int p = MOD) { return fpow(a, p - 2, p); }
inline int sign(long double x) { return x < -EPS ? -1 : x > +EPS; }
inline int sign(long double x, long double y) { return sign(x - y); }
mt19937 mt(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int myrand() { return abs((int)mt()); }
void chemthan() {
  long long n, l, r, k;
  cin >> n >> l >> r >> k;
  long long d = r - l + 1;
  if (d <= 0) d += n;
  if (d == n) {
    long long res = -1;
    for (long long x = 1; x * x <= k; x++) {
      if (k % x == 0) {
        long long y = k / x;
        for (long long z : {x, y}) {
          if (n <= z && z <= n + n) {
            chkmax(res, z - n);
          }
        }
      }
    }
    for (long long x = 1; x * x <= k + 1; x++) {
      if ((k + 1) % x == 0) {
        long long y = (k + 1) / x;
        for (long long z : {x, y}) {
          if (n < z && z <= n + n) {
            chkmax(res, z - n);
          }
        }
      }
    }
    cout << res << "\n";
    return;
  }
  int lim = 1e6;
  if (n <= lim) {
    for (long long t = n; t >= 0; t--) {
      long long rr = k % (n + t);
      if (d + max(1LL, t - n + d) - 1 <= rr && rr <= d + min(d, t)) {
        cout << t << "\n";
        return;
      }
    }
    cout << -1 << "\n";
    return;
  }
  long long res = -1;
  for (int i = (0); i < (lim + 1); ++i) {
    long long lo = max(n, k / (i + 1) + 1) - n;
    long long hi = (i ? min(n + n, k / i) : n + n) - n;
    if (lo <= hi) {
      long long u = lo - 1;
      long long v = hi;
      while (u < v) {
        long long w = u + v + 1 >> 1;
        if (d + max(1LL, w - n + d) - 1 <= k - (n + w) * i) {
          u = w;
        } else {
          v = w - 1;
        }
      }
      long long w = u + v >> 1;
      if (w > lo - 1 && k - (n + w) * i <= d + min(d, w)) {
        chkmax(res, w);
      }
    }
  }
  cout << res << "\n";
}
int main(int argc, char* argv[]) {
  ios_base::sync_with_stdio(0), cin.tie(0);
  if (argc > 1) {
    assert(freopen(argv[1], "r", stdin));
  }
  if (argc > 2) {
    assert(freopen(argv[2], "wb", stdout));
  }
  chemthan();
  cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
  return 0;
}
