#include <bits/stdc++.h>
int count(int *cc, int l, int r) {
  static char used[24];
  int i, cnt;
  memset(used, 0, sizeof used);
  cnt = 0;
  for (i = l; i <= r; i++)
    if (!used[cc[i]]) {
      used[cc[i]] = 1;
      cnt++;
    }
  return cnt;
}
int main() {
  static int cc[(24 * 4)];
  int a, b, ab, d, l, r, m, k0, k1, k2, k3, k, h, min;
  scanf("%d%d%d%d", &a, &b, &l, &r);
  l--, r--;
  ab = a + b;
  m = 4;
  h = l / ab;
  r -= h * ab;
  l -= h * ab;
  h = (r - l + 1) / ab;
  if (h > 2) r -= (h - 2) * ab;
  d = a > b ? a - b : 1;
  for (h = 0; h < m; h++) {
    for (k = 0; k < a - d; k++) cc[h * ab + k] = k;
    for (k = 0; k < d; k++)
      cc[h * ab + a - d + k] = h % 2 == 0 ? a - d + k : a + k;
  }
  min = a + a;
  for (k0 = 1; k0 <= d; k0++) {
    for (k = 0; k < b; k++) cc[ab * 0 + a + k] = cc[ab * 0 + a - k0];
    for (k1 = 1; k1 <= d; k1++) {
      for (k = 0; k < b; k++) cc[ab * 1 + a + k] = cc[ab * 1 + a - k1];
      for (k2 = 1; k2 <= d; k2++) {
        for (k = 0; k < b; k++) cc[ab * 2 + a + k] = cc[ab * 2 + a - k2];
        for (k3 = 1; k3 <= d; k3++) {
          int cnt;
          for (k = 0; k < b; k++) cc[ab * 3 + a + k] = cc[ab * 3 + a - k3];
          if (min > (cnt = count(cc, l, r))) min = cnt;
        }
      }
    }
  }
  printf("%d\n", min);
  return 0;
}
