#!/usr/bin/env python3
"""Project Euler Problem 2: Find sum of even Fibonacci numbers below 4,000,000."""

def sum_even_fibs(limit: int) -> int:
    """Return sum of even Fibonacci numbers less than limit."""
    a, b = 1, 2
    total = 0
    while b < limit:
        if b % 2 == 0:
            total += b
        a, b = b, a + b
    return total

if __name__ == "__main__":
    limit = 4_000_000
    result = sum_even_fibs(limit)
    print(f"Sum of even Fibonacci numbers below {limit}: {result}")

    # Verification assertion
    expected = 4613732
    assert result == expected, f"Expected {expected}, got {result}"
    print(f"VERIFIED: result matches expected value {expected}")