#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int a1,a2,n; cin >>a1>>a2>>n; int c = a2 - a1; int ans = (n - 1) * c + a1; cout << ans; return 0; }