#include <cstdio>
#include <cmath>
int main(){
    double C,Rin,Rout;
    scanf("%lf %lf %lf",&C,&Rin,&Rout);
    printf("%.6lf\n",C*M_PI*M_PI*(Rout+Rin)*(Rout-Rin)*(Rout-Rin)/4);
    
    return 0;
}