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)

// @prefix atcoder
// @description atcoder template

#include <bits/stdc++.h>
using namespace std;
#define int long long

// typedef
//------------------------------------------
typedef pair<int, int> PII;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef vector<PII> VP;

// rep
//------------------------------------------
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) (x).begin(), (x).end()
#define DEBUG(x) cerr << #x << ": " << x << '\n'
#define DEBUGP(x) cerr << #x << ": " << x.first << " \t" << x.second << '\n'
#define INF (1ll<<60)

int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
int lcm(int a, int b) { return a / gcd(a, b) * b; }
const int MOD = 1e9 + 7;


int a, b, c, k;

signed main()
{
	cin >> a >> b >> c >> k;

	int res = 0;
	if (k <= a){
		res = k;
	} else if (k <= a + b){
		res = a;
	} else {
		res = a - (c - (a + b + c - k));
	}

	cout << res << endl;
	return 0;
}