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)

#define _GLIBCXX_DEBUG
#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++)

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



int main() {
    long long A,B,C,K;

    cin >> A >> B >> C >> K;

    // for(int i=1; i<=K; i++){
    //     if(i<=A){
    //         sum++;
    //     }else if(i>(A+B) && i<=A+B+C){
    //         sum--;
    //     }
    // }

    if(K<=A){
        cout << K << endl;
    }else if(K <= A+B){
        cout << A << endl;
    }else{
        cout << A - (K - (A + B)) << endl;
    }
}