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 <algorithm>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <vector>

using namespace std;

typedef long long ll;
// constexpr ll MOD = 998244353;
constexpr ll MOD = 1000000007;

// struct UnionFind {
//     vector<ll> par;
//     vector<ll> siz;
    
//     UnionFind(ll N): par(N), siz(N,1) {
//         for (ll i=0;i<N;i++) par[i] = i;
//     }

//     ll root(ll x) {
//         if (par[x] == x) return x;
//         else return par[x] = root(par[x]);
//     }

//     void unite(ll x, ll y) {
//         ll rx = root(x);
//         ll ry = root(y);
//         if (rx == ry) return;
//         // if (siz[rx] < siz[ry]) swap(rx,ry);
//         par[rx] = ry;
//         siz[ry] += siz[rx];
//     }

//     bool same(ll x, ll y) {
//         ll rx = root(x);
//         ll ry = root(y);
//         return rx == ry;
//     }

//     ll size(ll x) {
//         return siz[root(x)];
//     }
// };

//     vector<ll> par;
//     vector<ll> siz;
    
//     UnionFind(ll N): par(N), siz(N,1LL) {
//         for (ll i=0;i<N;i++) par[i] = i;
//     }

//     ll root(ll x) {
//         if (par[x] == x) return x;
//         else return par[x] = root(par[x]);
//     }

//     void unite(ll x, ll y) {
//         ll rx = root(x);
//         ll ry = root(y);
//         if (rx == ry) return;
//         par[rx] = ry;
//         siz[ry] += siz[rx];
//     }

//     bool same(ll x, ll y) {
//         ll rx = root(x);
//         ll ry = root(y);
//         return rx == ry;
//     }

//     ll size(ll x) {
//         return siz[root(x)];
//     }
// };

int main(void) {
    int A, B, C, K;
    cin >> A >> B >> C >> K;
    int res = 0;
    if (A<K) {
        res += A;
    } else res += K;
    K -= A;
    K -= B;
    if (K>0) {
        res -= K;
    }
    cout << res << endl;

    return 0;
}