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;
using ull = unsigned long long;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define MOD 1000000007
#define PI 3.1415926535

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

    int sum = 0;
    if(a>=k){
        cout << k << endl;
        return 0;
    }

    if(a+b >= k){
        cout << a << endl;
        return 0;
    }

    sum = a;
    int n = k-a-b;
    sum -= n;
    cout << sum << endl;
    

    return 0;
}