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int find_closest(int A[], int N, int target) {
    if(target < A[0]) return A[0];
    if(target > A[N-1]) return A[N-1];
    int low = 0, high = N-1;
    while(low <= high) {
        int mid = low + (high - low) / 2;
        if(A[mid] == target) return target;
        else if(A[mid] < target) low = mid+1;
        else high = mid-1;
    } // after this step, if 'target' is still not found, 'low' is always a bit larger than 'target'
    if(A[low] - target < target - A[low-1])
        return A[low];
    else
        return A[low-1];
}