(C)
#include <cstdio>
int main()
{
	int n,m,k;launguage
    scanf("%d %d %d",&n,&m,&k);
    int a[k];
    a[0] = n;
    a[1] = m;
    if (k <= 2)
    {
        printf("%d",a[k - 1]);
        return 0;
    }
    for (int i = 2; i < k; i++)
        a[i] = a[i - 1] + (m - n);
    printf("%d",a[k]);
	return 0;
}