import math
def correlation(x, y):
n = len(x)
mean_x = sum(x) / n
mean_y = sum(y) / n
cov = sum((x[i] - mean_x) * (y[i] - mean_y) for i in range(n))
std_x = math.sqrt(sum((xi - mean_x) ** 2 for xi in x))
std_y = math.sqrt(sum((yi - mean_y) ** 2 for yi in y))
return cov / (std_x * std_y)
hours_studied = [1, 2, 3, 4, 5, 6, 7]
exam_score = [52, 58, 63, 68, 74, 77, 83]
r = correlation(hours_studied, exam_score)
print("r =", round(r, 3))