So the sum of the degrees of each vertex in G is 4m,

| v | = m, there are vertices with a degree of 3 in G. If no vertex has a degree greater than or equal to 5,

Then the sum of degrees of each vertex in G is less than or equal to 4m- 1, which is contradictory.

So at least one vertex in G has a degree greater than or equal to 5.