#include<iostream> #include<cstdio> #include<cstring> #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int a1,a2,n,b; cin>>a1>>a2>>n; b=a2-a1; cout<<a1+b*(n-1); return 0; }