pi=acos(-1.0)
https://www.luogu.org/problemnew/show/T4529
#include <cstdio> #include <cstdlib> #include <cmath> #include <cstring> #include <time.h> #include <string> #include <set> #include <map> #include <list> #include <stack> #include <queue> #include <vector> #include <bitset> #include <ext/rope> #include <algorithm> #include <iostream> using namespace std; #define ll long long #define minv 1e-6 #define inf 1e9 //#define pi 3.1415926536 #define E 2.7182818284 const ll mod=1e9+7;//998244353 const int maxn=1e5+10; int main() { int n,m; double pi=acos(-1.0); scanf("%d%d",&n,&m); printf("%.*f",m,pi*n); return 0; }