Then you may compute three sums:
S_1=x_1+...+x_997
S_2=x_1*x_1+...+x_997*x_997
S_3=x_1*x_1*x_1+...+x_997*x_997*x_997
to find out three sums for the missing three numbers. Then solve the equations to find them.
S_1=x_1+...+x_997
S_2=x_1*x_1+...+x_997*x_997
S_3=x_1*x_1*x_1+...+x_997*x_997*x_997
to find out three sums for the missing three numbers. Then solve the equations to find them.