public class String{
}

public class Geom{

    public void main(){
	int n, f;
	float circ;
	n = -1;
	while(n < 0) { printf ("Enter a positive integer: ");	
		    	   scanf ("%d", &n);
	}
	circ = 3.1415926 * n * 2;	
	printf("circumference of radius(%d) = %f\n", n, circ);
    } 
}