The 4th Bulgarian Army held the most important position for the conquest of Serbian Macedonia. The fighting began on 29-30 June 1913, between the 4th Bulgarian Army and the 1st and 3rd Serbian armies, first along the Zletovska and then after a Bulgarian retreat, along the Bregalnica. Internal confusions led to heavy Bulgarian losses in 1-3 July. The Serbs captured the whole 7th Division of the 4th Bulgarian Army, without any fight. By 8 July, the Bulgarian Army had been severely defeated. On the north the Bulgarians started to advance towards the Serbian border town of Pirot and forced Serbian Command to send reinforcements to the 2nd Army defending Pirot and Niš. This enabled Bulgarians to stop the Serbian offensive in Macedonia at Kalimanci on 18 July. On 13 July 1913, General Mihail Savov assumed control of the 4th and 5th Bulgarian armies. The Bulgarians dug into strong positions around the village of Kalimantsi, at the Bregalnica river in the northeastern Macedonia region. On 18 July, the Serbian 3rd army attacked, closing in on Bulgarian positions. The Bulgarians held firm, the artillery was very successful in breaking up the Serb attacks. If the Serbs had broken through the Bulgarian defences, they might have doomed the 2nd Bulgarian Army and driven out the Bulgarians entirely out of Macedonia. The defensive victory, along with the successes to the north of the 1st and 3rd armies, protected western Bulgaria from a Serbian invasion. Although this boosted the Bulgarians, the situation was critical in the south, with the Greek Army.. After the fighting begain on June 29-30 1913 approximately how many weeks lapsed before the 4th and 5th armies of Bulgaria fell?