If we look at the rules, we can observe that the sum of all the numbers on the board at any point of time either remains the same or gets reduced by 2 after each step. The sum of all the numbers written on the board initially was 157 i.e. an odd number. Hence, if we keep on subtracting either 0 or 2 from it repeatedly, we would get an odd number i.e. 1 in the end.