#include <stdio.h>
#define PI 3.141592653589793238
int main()
{
	int R;
	float c;
	printf("Enter radius \n");
	scanf("%d",&R);
	if(R>100 || R<1)
	{
		printf("Wrong Input");
		return 0;
	}
	c=2*PI*(float)(R);
	printf("Radius=%f",c);
}