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>
#include <iostream>
#include <utility>
#include <algorithm>
#include <numeric>
#define load ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)
using namespace std;
#define ll long long
#define ull unsigned long long
#define fori(i,n) for (int i=0; i<int(n);i++)
#define srt(v) sort(v.begin(), v.end())
#define MOD 1000000007
const int INF = 1e9;
const double PI = 3.14159265358979323846;

ll gcd(ll a, ll b) {
    return b != 0 ? gcd(b, a % b) : a;
}
 
ll lcm(ll a, ll b) {
    return (a * b) / gcd(a, b);
}

void solve(){
	
}

int main(){
	load;
    ll a,b,c,k;
    cin >> a >> b >> c >> k;
    if (k<=a){
    	cout << k << "\n";
    	return 0;
    }else if (k<=a+b){
    	cout << a << "\n";
    	return 0;
    }else{
    	cout << a+(k-a-b)*-1 << "\n";
    }
	return 0;
}