#include <bits/stdc++.h> using namespace std; int main() { int a1,a2,n; cin >> a1 >> a2 >> n; cout << (n - 1) * (a2 - a1) + a1; return 0; }

#include<bits/stdc++.h> using namespace std; int main() { int a1,a2,n,x; cin>>a1>>a2>>n; x=a1+(n-1)*(a2-a1); cout<<x; return 0; }