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>
typedef long long int ll;
#define rep(i,n) for (int i = 0; i< (n); i++)
#define Rep(i,n,m) for (int i = (n); i< (m); i++)
#define Sort(a) sort(a.begin(), a.end())
#define Reverse(a) reverse(a.begin(), a.end())
const int INF = 1e9;
const ll MOD = 1000000007;
const ll LINF = 1e18;
using namespace std;



int main()
{
    ll a, b, c, k,ans=0;
    
    cin>>a>>b>>c>>k;
    
    if(k>a){
        ans += a;
        
        k = k -a;
        if(k>b){
            k = k-b;
            ans -= k;
        }
        else{
        }
    }
    else{
        ans = k;
    }
    cout<<ans<<endl;
    return 0;
}