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)

// AtCoder165 C

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <math.h>
#include <assert.h>
#include <string.h>
#include <memory.h>
#include <malloc.h>
#include <stdlib.h>

// qsortで用いる比較用関数．*a<*bならaが先になる．
int compare(const void* a, const void* b) {
    return *(int*)a - *(int*)b;
}

int revcompare(const void* a, const void* b) {
    return *(int*)b- *(int*)a;
}

struct node_t{
    int value;
    struct node_t* left;
    struct node_t* right;
};

struct node_t* mallocNode(int adds) {
    struct node_t* add;

    add = (struct node_t*)malloc(sizeof(struct node_t));
    if (add == NULL) {
        return NULL;
    }

    add->left = NULL;
    add->right = NULL;
    add->value =  adds;

    return add;
}

int addNode(struct node_t* root, int tmps) {
    struct node_t* node;
    if (root == NULL) {
        root = mallocNode(tmps);
        return 0;
    }

    node = root;
    while (1) {
        if (tmps < node->value) {
            if (node->left == NULL) {
                node->left = mallocNode(tmps);
                return 0;
            }
            node = node->left;
        }
        else if (tmps > node->value) {
            if (node->right == NULL) {
                node->right = mallocNode(tmps);
                return 0;
            }
            node = node->right;
        }
        else {
            return 1; // 重複のときのみ1を返す
        }
    }

}


int main() {
    int i,j;
    int n;
    int a,b,c;
    int k;
    int sum = 0;

    scanf("%d %d %d %d", &a, &b, &c, &k);

    if(a<k){
        sum += a;
        k -= a;
    }else{
        sum += k;
        k = 0;
    }

    if(b<k){
        k -= b;
    }else{
        k = 0;
    }

    sum-=k;
    printf("%d", sum);
    return 0;

}