II: Tự luận
#include <bits/stdc++.h>
using namespace std;
double a,b,c,p,s;
int main()
{
freopen("dodai.inp","r",stdin);
freopen("dientich.out","w",stdout);
cin>>a>>b>>c;
p=(a+b+c)/2;
s=sqrt(p*(p-a)*(p-b)*(p-c));
cout<<fixed<<setprecision(1)<<p;
return 0;
}