#include <bits/stdc++.h>

using namespace std; double a,b,c,S,p;

int main() { cin>>a>>b>>c; if(a>0 and b>0 and c>0 and a+b>c and a+c>b and b+c>a){ p=0.5*(a+b+c); S=sqrt(p*(p-a)(p-b)(p-c)); printf("%.2f",S); }else{ cout<<"Data Error!"<<endl; }

return 0;

}