#include<stdio.h>

int main(){

    char s[105];
    scanf("%s", s);
    // printf("%s", s);
    // 1+3+...


    int diff = abs((s[0]-s[2]));
    //printf("%d", diff);

    // diff ok

    int n;
    scanf("%d", &n);

    int arr[n];
    arr[0] = s[0];
    arr[1] = s[2];

    for (int i=2; i<n; i++){
        arr[i] = (arr[i-1]+ diff);
    }

    /*for (int i=0; i<n; i++){
        printf("%c ", arr[i]);
    }*/

    // above ok

    int total=0;

    for (int i=0; i<n; i++){
        total += arr[i]-48;
    }


    printf("%d", total);

}