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 REP(i, n) for(int i = 0; i < n; i++)
#define REP1(i,n) for(int i = 1; i < n+1 ;i++)
#define REPR(i, n) for(int i = n; i >= 0; i--)
#define FOR(i, m, n) for(int i = m; i < n; i++)
#define INF 2e9
#define ALL(v) v.begin(), v.end()
#define SZ(x) ((int)(x).size())
#define ARRAY_LENGTH(array) (sizeof(array) / sizeof(array[0]))
using namespace std;
typedef long long ll;
using p = pair<int, int>;
using P = pair<ll, ll>;
using V = vector<int>;
using VV = vector<vector<int>>;
using VVV = vector<vector<vector<int>>>;
using VL = vector<ll>;
using VVL = vector<vector<ll>>;
using VVVL = vector<vector<vector<ll>>>;
using Graph = VV;


int main(){
    ios::sync_with_stdio(false); cin.tie(0);
    ll a,b,c,k;
    cin >> a >> b >> c >> k;
    ll ans = 0;
    if(k>=a){
        if(k>=a+b){
            if(k>=a+b+c){
                ans = a-c;
            }
            else ans =a-((k-a-b));
        }
        else ans = a;
    }
    else ans = k;



    cout << ans << endl;


}