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 inf             0x3f3f3f3f
#define INF             2e18
#define eps             1e-9

#define FastRead        ios_base::sync_with_stdio(0);cin.tie(0)
#define fRead           freopen("input.txt","r",stdin)
#define fWrite          freopen("output.txt","w",stdout)

#define LL              long long
#define ull            unsigned long long
#define PI              acos(-1.0)
#define pb              push_back
#define mk              make_pair
#define pii             pair<int,int>
#define pLL             pair<LL,LL>
#define ff              first
#define ss              second
#define all(a)          a.begin(),a.end()
#define SQR(a)          ((a)*(a))
#define min3(a,b,c)     min(a,min(b,c))
#define max3(a,b,c)     max(a,max(b,c))
#define min4(a,b,c,d)   min(min(a,b),min(c,d))
#define max4(a,b,c,d)   max(max(a,b),max(c,d))
#define max5(a,b,c,d,e) max(max3(a,b,c),max(d,e))
#define min5(a,b,c,d,e) min(min3(a,b,c),min(d,e))
#define vi              vector <int>
#define vL              vector <LL>
#define LB(a,x)         (lower_bound(all(a),x)-a.begin()) //  first element in the range [first,last) which does not compare less than val.
#define UB(a,x)         (upper_bound(all(a),x)-a.begin()) //  first element in the range [first,last) which compares greater than val.
#define prec(n)         fixed << setprecision(n)

#define MEM(a,x)        memset(a,x,sizeof(a))
#define SORT(v)         sort(v.begin(),v.end())
#define REV(v)          reverse(v.begin(),v.end())
#define Unique(a)       sort(all(a)),a.erase(unique(all(a)),a.end())

#define FOR(i,a,b)      for(int i=a;i<=b;i++)
#define ROF(i,a,b)      for(int i=a;i>=b;i--)
#define REP(i,b)        for(int i=0;i<b;i++)
#define IT(it,x)	    for(it=x.begin();it!=x.end();it++)
int main()
{
    LL a,b,c,k;
    cin>>a>>b>>c>>k;
    LL ans=0;
    ans=min(a,k);
    k-=min(k,a);
    k-=min(k,b);

    ans-=min(k,c);
    cout<<ans;


}