Problem:
Score : 200 points

Problem Statement

We have A cards, each of which has an integer 1 written on it. Similarly, we also have B cards with 0s and C cards with -1s.

We will pick up K among these cards. What is the maximum possible sum of the numbers written on the cards chosen?

Constraints

All values in input are integers.

0 \leq A, B, C

1 \leq K \leq A + B + C \leq 2 \times 10^9

Input

Input is given from Standard Input in the following format:

A B C K

Output

Print the maximum possible sum of the numbers written on the cards chosen.

Sample Input 1

2 1 1 3

Sample Output 1

2

Consider picking up two cards with 1s and one card with a 0.
In this case, the sum of the numbers written on the cards is 2, which is the maximum possible value.

Sample Input 2

1 2 3 4

Sample Output 2

0

Sample Input 3

2000000000 0 0 2000000000

Sample Output 3

2000000000

Solution in C (GCC 9.2.1) (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void) {
  int a, b, c, k, nokori;
  scanf("%d %d %d %d", &a, &b, &c, &k);
  if (k <= a) {
    printf("%d\n", k);
    exit(0);
  } else {  // k>aの時 bも使うか判定
    nokori = k - a;
    if (nokori <= b) {  // bも使うならaだけ
      printf("%d\n", a);
    } else {  // cも使うなら
      nokori = nokori - b;
      printf("%d\n", a - nokori);
      exit(0);
    }
  }
  return 0;
}