using namespace std;
int n,m,me;
int main(){
	cin>>n>>m>>me;
	if(me==1) cout<<(n+m+13)/2;
	else cout<<(n+m-13)/2;
}

#include<bits/stdc++.h> using namespace std; int main() { int f,m,n; cin>>f>>m>>n; if(n==1)cout<<(f+m+13)/2; else cout<<(f+m-13)/2;

return 0;

}