In 1916 Romania entered World War I on the side of the Allies. In doing so, Romania's goal was to unite all the territories with a Romanian national majority into one state. In the Treaty of Bucharest , terms for Romania's acquisition of territories within Austria-Hungary were stipulated. In 1918, after the October Revolution, the Bolsheviks signed a separate peace with the Central Powers in the Treaty of Brest-Litovsk. Romania was alone on the Eastern Front, a situation that far surpassed its military capabilities. Therefore, on 7 May 1918, Romania sued for peace. The prime minister of Romania, Alexandru Marghiloman, signed the Treaty of Bucharest  with the Central Powers. However, this treaty was never signed by King Ferdinand of Romania. At the end of 1918 Romania's situation was dire. She was suffering from the consequences of punitive war reparations. Dobruja was under Bulgarian occupation. The German army under the command of Field Marshal August von Mackensen was retreating through Romania. The bulk of the Romanian army was demobilized, leaving only four full-strength divisions. A further eight divisions were left in a reserve status. The four battle-ready divisions were used to keep order and protect Basarabia from possible hostile actions of the Soviet Union. On 10 November 1918, taking advantage of the Central Powers' precarious situation, Romania re-entered the war on the side of the Allied forces, with similar objectives to those of 1916. King Ferdinand called for the mobilization of the Romanian army and ordered it to attack by crossing the Carpathian Mountains into Transylvania. The end of World War I that soon followed did not bring an end to  fighting for the Romanian army. Its action continued into 1918 and 1919 in the Hungarian-Romanian war.
Question: How many years was it from the first time Romania entered World War I, to the time they re-entered the war?
Answer: 2