#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    double A,B;
    cin >> A >> B;
    printf("%.9lf\n", 2 * M_PI * (B - A) );
}