#include<stdio.h>
#define pi 3.1416
int main()
{
    int R;
    float circumference;
    printf("enter radius: ");
    scanf("%d",&R);
    circumference=2*pi*R;
    if(1<=R&&R<=100)
    printf("circumference of a cycle=%f",circumference);
    else
    return 0;
}
