#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>

using namespace std;




int main(){
    int c,r1,r2;
    
    scanf("%d%d%d",&c,&r1,&r2);
    
    int d = (r2-r1)*(r2-r1)*(r2+r1)*c;
    
    printf("%.10lf\n",d/4.0*3.1415926538*3.1415926538);
    
    return 0;
}