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 <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <math.h>
#include <iomanip>
#include <bitset>
#include <cstring>
#include <stdlib.h>
#include <utility>
#include <set>
#include <map>
#include <string.h>
#include <cstring>
#include <queue>
 
using namespace std;

int n, k;
vector<int> a(n);
bool dfs(int i, int sum){
    if(i==n) return sum == k;
    
    if(dfs(i+1, sum)) return true;
    
    if(dfs(i+1, sum+a[i])) return true;
    
    return false;
}

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