#include<iostream> using namespace std; int main(){/** int a,b,temp; cin>>a>>b; temp=a; a=b; b=temp; cout<<a<<" "<<b; char A; cin>>A; cout<<(A+10-30)*20/5;**/ int a1,a2,n; cin>>a1>>a2>>n; cout<<a1+(n-1)*(a2-a1); return 0; }