How many men lapped the water and were kept for Gideon's army?

Answer: 300

The LORD sifted Gideon's men at the water: "With the three hundred men who lapped the water I will save you."

“And the number of those who lapped the water with their hands to their mouths was three hundred men; all the others knelt to drink. Then the LORD said to Gideon, “With the three hundred men who lapped the water I will save you and deliver the Midianites into your hand. But all the others are to go home.””— Judges 7:6-7 (BSB)