On 2 May, 1687, a Russian army of about 132,000 soldiers, led by knyaz Vasily Golitsyn, left Okhtyrka on the Belgorod Line. On 30 May they were joined by 50,000 Left Bank Cossacks under hetman Ivan Samoilovich at the mouth of the Samora River where the Dnieper turns south. In the heat of summer, 180,000 men, 20,000 wagons and 100,000 horses set out down the east bank of the Dnieper. The huge force, which started too late and was perhaps not well organized,  could only travel about 10km per day. When the Russians reached the Konskiye Vody river on the west-flowing part of the Dnieper, they found that the Tatars has set fire to the steppe . After a few days of marching over burnt land, their horses were exhausted, they were short of water and 130 miles from their goal at Perekop, however Golitsyn built a fortress at Novobogoroditskoe at the junction of the Dnieper and the Samara. On 17 June they decided to turn back.
Question: How many days did the Russian army travel before being joined by the Left bank Cossacks?
Answer: 28