11*12 *13 * has two zeros at the end ... * 20.

2 1 * 22 * 23 * ...* 30 has three zeros at the end.

There are two zeros at the end of 3 1 * 32 * 33 * ...* 40.

4 1 * 42 * 43 * ...* 50 has four zeros at the end.

2+2+3+2+4= 13

Multiply several natural numbers 1, 2, 3 ... If it is known that the last thirteen bits of this product are all exactly 0, then the smallest natural number that finally appears should be 50.