utility function to find pow ( base , exponent ) % modulus
function pow1 ( base1 , exponent , modulus ) { let result = 1 ; base1 = base1 % modulus ; while ( exponent > 0 ) { if ( exponent % 2 == 1 ) result = ( result * base1 ) % modulus ; exponent = exponent >> 1 ; base1 = ( base1 * base1 ) % modulus ; } return result ; }