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>
using namespace std;
                     
#define int             long long
#define ld              long double
#define mp              make_pair
#define ff              first
#define ss              second
#define pb              push_back
#define fo(i,n)         for(i=0;i<n;i++)
#define fo1(i,n)        for(i=1;i<=n;i++)
#define FO(i,k,n)       for(i=k;k<=n?i<=n:i>=n;k<=n?i++:i--)
#define all(c)          c.begin(),c.end()
#define rall(c)         c.rbegin(),c.rend()
#define si              set<int>
#define vi              vector<int>
#define mii             map<int,int>
#define pii             pair<int,int>
#define vpii            vector<pii>
#define vvi             vector<vi>
#define usi             unordered_set<int>
#define umii            unordered_map<int,int>
#define pqmx            priority_queue<int>
#define pqmn            priority_queue<int,vi,greater<int> >
#define sp(x)           cout<<setprecision(x)<<fixed;
#define setbits(x)      __builtin_popcountll(x)
#define zerobits(x)     __builtin_ctzll(x)
#define in(a,n)         vi a(n);fo(i,n)cin>>a[i];
#define in1(a,n)        vi a(n+1);fo1(i,n)cin>>a[i];
#define w(t)            int t;cin>>t;while(t--)
#define gcd             __gcd
#define lcm(x,y)        x*(y/gcd(x,y))
#define endl            '\n'
#define PI              3.14159265358979323846
const int inf =         1e18;
const int mod =         1e9+7;
void __p(int x) {cout<<x;}
void __p(int32_t x){cout<<x;}
void __p(float x){cout<<x;}
void __p(double x){cout<<x;}
void __p(ld x) {cout<<x;}
void __p(char x){cout <<'\''<<x<<'\'';}
void __p(const char *x){cout <<'\"' <<x<<'\"';}
void __p(const string &x) {cout<<'\"'<<x<<'\"';}
void __p(bool x) {cout<<(x?"true":"false");}
void _p() {cout << "]\n";}
template<typename T,typename V>     void __p(const pair<T,V> &x) {cout<<'{';__p(x.first);cout<<',';__p(x.second);cout<<'}';}
template<typename T>                void __p(const T &x) {int f = 0; cout << '{'; for (auto &i: x) cout << (f++ ? "," : ""), __p(i); cout << "}";}
template <typename T,typename... V> void _p(T t, V... v) {__p(t);if(sizeof...(v))cout<<", ";_p(v...);}
int po(int x,int p,int m = inf) {int ans=1;x%=m;while(p>0){if(p&1)ans=(ans*x)%m;p=p>>1;x=(x*x)%m;}return ans;}
int inv(int x,int m=mod){return po(x,m-2,m)%m;}
#ifndef ONLINE_JUDGE
#define dbg(x...) cout<<"["<<#x<<"]=[";_p(x)
#else 
#define dbg(x...)
#endif
//=================================================================================




const int N=1e6+6;
int n,m,k,x,y,z,a,b,c,d,i,j,l,r;








void sol()
{   
    cin>>a>>b>>c>>k;
    if(a>=k)cout<<k;
    else if(b>=k-a)cout<<a;
    else cout<<a-(k-a-b);
    
    
    
    //cout<<  <<endl;
}





int32_t main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    //sp(10);
    // w(t)
    sol();
    return 0;
}