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;
typedef long long ll;

// マクロ
// forループ
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define REPD(i,n) for(ll i=n-1;i>=0;i--)
#define FOR(i,a,b) for(ll i=(a);i<=(ll)(b);i++)
#define FORD(i,a,b) for(ll i=(a);i>=(ll)(b);i--)
// xにはvectorなどのコンテナ
#define ALL(x) (x)begin(),(x).end()
#define SIZE(x) ((ll)(x).size())
#define MAX(x) *max_element(ALL(x))
#define MIN(x) *min_element(ALL(x))
// 出力
#define PRINT(x) cout<<(x)<<endl
#define PRINTA(x,n) REP(i,n)PRINT(x[i])
// 定数
#define INF 1000000000000 // 10^12
#define MOD 1000000007 // 10^9+7
// 略記
#define PB push_back
#define MP make_pair



int main() {
    int A, B, C, K;
    cin >> A >> B >> C >> K;
    int ans = 0;
    if (K <= A) {
        ans = K;
    } else if (K <= A + B) {
        ans = A;
    } else {
        ans = A - (K - A - B);
    }
    PRINT(ans);
    return 0;
}