#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    double a, b, ans = 0, cnt = 0;
    cin >> a >> b;
    for(double i = a; i <= b; i += 0.000001){
        ans += 1 - abs(i);
        cnt++;
    }
    ans *= 4 * M_PI * 0.000001;
    cout << fixed << setprecision(15) << ans << '\n';
}