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 <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = s; i < (int)(n); i++)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()

using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

//const ll INF = 1e18L + 5;
//const int INF = 1e9 + 5;
//const double pi = 3.14159265358979323846;

void	solve()
{
	ll a, b, c, k;
	cin >> a >> b >> c >> k;
	ll ans = 0;
	if (k <= a)
		cout << 1 * k << endl;
	else {
		ans += a;
		k -= a;
		if (k <= b)
			cout << ans << endl;
		else {
			k -= b;
			cout << ans + (-1 * k) << endl;
		}
	}
}

int		main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);

	solve();
}