#include #define FOR(i,a,b) for (int i=(a);i<(b);i++) #define FORR(i,a,b) for (int i=(a);i>=(b);i--) #define pb push_back #define pcnt __builtin_popcount #define show(x) cout<<#x<<" = "< pii; typedef vector vi; typedef vector vvi; typedef vector vpii; typedef set si; typedef pair pll; typedef vector vl; typedef vector vvl; typedef vector vpll; typedef set sl; templatestring join(vector&v) {stringstream s;FOR(i,0,sz(v))s<<' '<b)swap(a,b);for(;a>0;b%=a,swap(a,b));return b;} int modpow(ll a,ll n,int m){if(a==0)return a;ll p=1;for(;n>0;n/=2,a=a*a%m)if(n&1)p=p*a%m;return(int)p;} void dout(double d){printf("%.12f\n",d);} const int iinf = 1e9; const ll linf = 1e18; const int mod = 1e9+7; const double pi = acos(-1); const double eps = 1e-10; main(){ cin.tie(0); ios::sync_with_stdio(false); double a, b; cin >> a >> b; dout(pi * 2 * (b-a)); return 0; }