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 <iostream>
#include <iomanip> //! for setprecision(10)
#include <math.h>
#include <algorithm>
#include <functional> 
#include <string>
#include <vector>

#include <cstring>
#include <set>
#include <map>
#include <queue>
#include <utility>

using namespace std;

typedef long long LL;

#define dump(c) { for (auto it = c.begin(); it != c.end(); ++it) if (it == c.begin()) cout << *it; else cout << ' ' << *it; cout << endl; } 
#define rep(i,n) for (int i = 0; i < (n); ++i)

const int MOD = 1000000007;

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

    int A, B, C, K;
    cin >> A >> B >> C >> K;

    int a = min(A, K);
    int b = min(B, K-a);
    int c = K-a-b;

    cout << (a-c) << endl;

    return 0;
}