#include <stdio.h>
#define PI 3.141592653589793238462643383279
int main ( int argc , char * argv[] ) {
int l;
scanf("%d" , &l);
while ( l != 0 ) {
printf("%.2llf\n" , ( PI * (long double)(l/PI) * (long double)(l/PI) ) / 2 );
scanf("%d" , &l);
}
return 0;
}
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