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>
#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define ll long long
#define ll_MAX LONG_LONG_MAX
#define ll_MIN LONG_LONG_MIN
#define pi pair<ll,ll>
#define endl "\n"
#define MAXN 100005
using namespace std;

ll a,b,c,k;

void solve()
{
	cin>>a>>b>>c>>k;
	ll sum=0;
	if(k>a)
	{
		k-=a;sum+=a;
	}
	else
	{
		cout<<k<<endl;return;
	}
	if(k>b)
	{
		k-=b;
	}
	else
	{
		cout<<sum<<endl;return;
	}
	cout<<sum-k<<endl;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
	cout.tie(NULL);
    solve();
}