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 <stdio.h>

int main(void){
    int A,B,C,K,ans=0;
    scanf("%d %d %d %d",&A,&B,&C,&K);

    //aとKの枚数を比較する
    //kがa以上だった場合、とりあえず答えにaの値を加算し、kの枚数をaだけ減らす
    //kがaより小さいなら、とりあえずaの値をkだけ増やす。
    if(A<=K){
        ans += A;
    }else{
        ans += K;
    }

    //kからaとbの枚数だけ減らす
    K -= (A + B);

    //もしまだkが1以上あるのなら、その枚数だけ答えから引く
    if(K>0){
        ans -= K;
    }

    printf("%d\n",ans);
    return 0;
}