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 assn(n,a,b) assert(n<=b && n>=a)
using namespace std;
#define pb push_back
#define mp make_pair
#define clr(x) x.clear()
#define sz(x) ((int)(x).size())
#define F first
#define S second
#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,b) for(i=0;i<b;i++)
#define rep1(i,b) for(i=1;i<=b;i++)
#define pdn(n) printf("%d\n",n)
#define sl(n) scanf("%lld",&n)
#define sd(n) scanf("%d",&n)
#define pn printf("\n")
typedef pair<int,int> PII;
typedef vector<PII> VPII;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef long long LL;
#define MOD 1000000007
LL mpow(LL a, LL n)
{LL ret=1;LL b=a;while(n) {if(n&1)
    ret=(ret*b)%MOD;b=(b*b)%MOD;n>>=1;}
return (LL)ret;}
#define MAXK 100000
#define MAXN 1000000000
int ar[MAXK];
typedef unsigned long long int ULL;
#define SSTR( x ) static_cast< std::ostringstream & >( \
        ( std::ostringstream() << std::dec << x ) ).str()
bool isSafe(int r, int c, vector<vector<int> > arr) {
	int n = arr.size();
	int m = arr[0].size();
	return (r>=0 && r<n && c>=0 && c<m);
}
LL gcd(LL a,LL b){if(b==0) return a;a%=b;return gcd(b,a);} 
/////////////////////////////////////////////////////////////

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    LL i,j,k,l,n,m,q,d,a,b,c,ans,tot,mx=INT_MIN,mn=INT_MAX;
    cin>>a>>b>>c>>k;
    tot=0;
    if(k<=a) tot=k;
    else {
    	tot=a;
    	if(k>a+b) {
    		tot -= k-a-b;
    	}
    }
    cout<<tot;
    
    
    return 0;
}