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 <iostream>
#include <vector>
#include <cmath>
#include <typeinfo>
#include <set>
#include <bitset>
#include <string>
#include <map>
#include <algorithm>
#include <iomanip>
#include <numeric>
using namespace std;
typedef long long ll;

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