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>
using namespace std;
using ll = long long;

int main()
{
    ll a, b, c, k;
    cin >> a >> b >> c >> k;

    ll ans = 0;

    bool finish = false;

    if (k == a)
    {
        ans = a;
        finish = true;
    }
    else if (k > a)
    {
        ans += a;
        k = k - a;
    }
    else if (k < a)
    {
        ans += k;
        finish = false;
    }

    if (k == b && !finish)
    {
        finish = true;
    }
    else if (k > b && !finish)
    {
        k = k - b;
    }
    else if (k < b && !finish)
    {
        finish = true;
    }

    if (k == c && !finish)
    {
        ans -= c;
        finish = true;
    }
    else if (k > c && !finish)
    {
        ans -= c;
        k = k - c;
    }
    else if (k < c && !finish)
    {
        ans -= k;
        finish = true;
    }

    cout << ans << endl;
}