#include<iostream>

using namespace std;

int main()
{int x,y,z,s=0;
 cin>>x>>y>>z;
 s=x+y+z;
 while(x+y!=z)
 { x=y;
   y=z;
   cin>>z;
   s=s+z;
 } 
 cout<<s;
 system("pause");
 return 0;
}