#include<iostream>
#include<iomanip>
using namespace std;
const double pi = 3.14;

int main(){
    int r1,r2;
    cin>>r1>>r2;
    
    cout<<fixed<<setprecision(2)<< pi * r1 *r1 - pi * r2*r2;
    return 0;
}

题解：

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

int main(){
    long long a,b;
    cin>>a>>b;
    printf("%0.2lf",a*a*3.14-b*b*3.14);
    return 0;
}

#include<iostream>
#include<iomanip>
using namespace std;
const double pi = 3.14;

int main(){
    int r1,r2;
    cin>>r1>>r2;
    
    cout<<fixed<<setprecision(2)<< pi * r1 *r1 - pi * r2*r2;
    return 0;
}