#include <iostream> #include <cmath> #include <iomanip> using namespace std; int main(){ int a,b,c,s; cout<<"enter three number"<<endl; cin>>a>>b>>c; if(a+b>c&&a+c>b&&b+c>a){ s=(a+b+c)/2; cout<<s<<endl; }else{ cout<<"it is not a trilateral!"<<endl; } return 0; }