/*
#include <stdio.h>
#include <stdlib.h>
int main()
{
int i, n;
scanf("%d",&n);
for(i=1; i<=9; i++)
{
printf("%d*%d=%d\n",n, i,n*i );
}
}
#include <stdio.h>
int main()
https://codeup.kr/problem.php?id=1075{
int i, n;
scanf("%d",&n);
https://codeup.kr/upload/pimg6205_1.png
for(i=1;i<=n;i++){
if(i%3!=0)
printf("%d ",i);
}
}https://codeup.kr/upload/pimg6205_1.png
*/
#include <stdio.h>
int main()
{
int i, n,a,d;
scanf("%d %d %d",&a,&d,&n);
for(i=1; i<n; i++)
{
a = a+d;
}
printf("%d",a);
}