#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
    ios_base::sync_with_stdio(false);
    string A, B;
    int repeat;
    cin >> A >> B >> repeat;


    string s = "";
    for(int i = 0; i < repeat; i++) {
        s += A;
        if(A.size() > 0) {
            A.erase(A.end() - 1);
        }
    }
    vector<bool> alpha(26, false);
    for(int i = 0; i < B.size(); i++) {
        alpha[B[i] - 'a'] = true;
    }
    int result = 0;

    for(int i = 0; i < s.size(); i++) {
        int sum = 0;
        for(int j = i; j < s.size(); j++) {
            sum += alpha[s[j] - 'a'];
            result += sum;
        }
    }
    cout << result << endl;
    return 0;
}