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 ios ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
typedef long long ll;
#define pb push_back
#define ins insert
#define pll pair<ll,ll>
#define fi first
#define se second
#define mpr make_pair
#define vtr vector
#define itor iterator 
#define N ll(1e9+7)
#define endl '\n'
#define cont continue
using namespace std;
//ll power(ll a,ll b,ll mod)
//{
//	if(b==0)return 1;
//	ll ans=1;
//	while(b>0)
//	{
//		if(b&1)ans=(ans*a)%mod;
//		a=(a*a)%mod;
//		b>>=1;
//	}
//	return ans;
//}
int main()
{
	ll a,b,c,k;
	cin>>a>>b>>c>>k;ll ans;
	if(k<=a)
	{
		ans=k;
	}
	else if(k<=a+b)
	{
		ans=a;
	}
	else
	{
		ans=a;
		ans-=(k-(a+b));
	}cout<<ans;
}