Step 1 :
Divide $ 1000000 $ by $ 777777 $ and get the remainder

$$ 1000000 : 777777 = 1 \text{ ( remainder is } \color{blue}{ 222223 } \text{ ) } $$

The remainder is positive ($ 222223 > 0 $), so we will continue with division.

Step 2 :
Divide $ 777777 $ by $ \color{blue}{ 222223 } $ and get the remainder

$$ 777777 : 222223 = 3 \text{ ( remainder is } \color{blue}{ 111108 } \text{ ) } $$

The remainder is still positive ($ 111108 > 0 $), so we will continue with division.

Step 3 :
Divide $ 222223 $ by $ \color{blue}{ 111108 } $ and get the remainder

$$ 222223 : 111108 = 2 \text{ ( remainder is } \color{blue}{ 7 } \text{ ) } $$

The remainder is still positive ($ 7 > 0 $), so we will continue with division.

Step 4 :
Divide $ 111108 $ by $ \color{blue}{ 7 } $ and get the remainder

$$ 111108 : 7 = 15872 \text{ ( remainder is } \color{blue}{ 4 } \text{ ) } $$

The remainder is still positive ($ 4 > 0 $), so we will continue with division.

Step 5 :
Divide $ 7 $ by $ \color{blue}{ 4 } $ and get the remainder

$$ 7 : 4 = 1 \text{ ( remainder is } \color{blue}{ 3 } \text{ ) } $$

The remainder is still positive ($ 3 > 0 $), so we will continue with division.

Step 6 :
Divide $ 4 $ by $ \color{blue}{ 3 } $ and get the remainder

$$ 4 : 3 = 1 \text{ ( remainder is } \color{blue}{ 1 } \text{ ) } $$

The remainder is still positive ($ 1 > 0 $), so we will continue with division.

Step 7 :
Divide $ 3 $ by $ \color{blue}{ 1 } $ and get the remainder

$$ 3 : \color{blue}{ \boxed { 1 }} = 3 \text{ ( remainder is } \color{blue}{ 0 } \text{ ) } $$

The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 1 }} $.

This solution can be visualized using a Venn diagram.

The GCD equals the product of the numbers at the intersection.

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