#define _USE_MATH_DEFINES
#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
#include <math.h>
 
void CountCircumReference()
{
	long double circleRadius, circumReference;
	while (1)
	{
		printf("Enter the radius of the cirlce \n");
		scanf("%Lf", &circleRadius);
		if (circleRadius <= 100 && circleRadius >= 1)
		{
			break;
		}
		printf("Wrong input \n");
	}
 
	circumReference = 2 * M_PI * circleRadius;
	printf("%Lf \n", circumReference);
 
	return;
}
 
int main(int argc, const char* argv[])
{
	CountCircumReference();
 
	return 0;
}