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++ (Clang 10.0.0) (judge verdict: Accepted)

#include <iostream>
#include <vector>
#include <numeric>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <string>
#include <cstring>
#include <queue>
#define myfor(i,N) for(i=0;i<N;i++)
#define myforFL(i,f,l) for(i=f;i<l;i++)
#define myforInv(i,N) for(i=N;i>=0;i--)
#define myforFLInv(i,f,l) for(i=f;i>l;i--)

using namespace std;

int main(){
	long A,B,C,K;
	cin >> A >> B >> C >> K;
	if(A>=K)cout << K << endl;
	else if(A+B >= K) cout << A << endl;
	else cout << A - (K -(A+B)) << endl;

	return 0;
}