// sample prelim question (just blanks)

public class rms {

    public static void main(String[] args) {

	// Initialize data:
	TokenReader in = new TokenReader(System.in);
	int n = in.readInt();   // # of molecules
	double sum = 0.0;       // sum of speeds so far
	double squares = 0.0;   // sum of squared speeds so far
	int k = 0;              // # of speeds already processed
	double speed;		// speed of a molecule

	// Compute sum of speeds and sum of squared speeds:
	while( k !=n ) {
	    speed = in.readDouble();             // Read next speed
	    sum += speed;	                 // Sum speeds
	    squares = squares + speed*speed;	 // Sum squared speeds
	    ++k;	                         // Increment # of speeds
	}

	// Report if zero molecules, or report percent error of Vrms from Vmean
	if (n==0) 
	    System.out.println("No molecules!");
	else {
	    double Vmean = sum/n;               // mean speed
	    double Vrms = Math.sqrt(squares/n); // rms speed
	    System.out.println("Percent error:" + 
			       Math.abs(100*(Vrms-Vmean)/Vmean));
	}
    }
}