#include <iostream>
#include <string>

using namespace std;

int l = 0;
int lans = 0 , rans = 1000000000;
int cur = 0;
int k;
int a[26];
string s;

int main()
{

    cin >> s;
    cin >> k;

    for (int r = 0; r < s.length(); r++){
        if (++a[s[r] - 'a'] == 1) cur++;

        while (cur > k){
            if (--a[s[l] - 'a'] == 0) cur--;
            l++;
        }

        while (cur == k){
            if (a[s[l] - 'a'] > 1){
                a[s[l] - 'a']--;
                l++;
            }
            else{
                break;
            }
        }

        if (cur == k){
            if (rans - lans + 1 > r - l + 1){
                lans = l;
                rans = r;
            }
        }
    }

    if (rans == 1000000000){
        cout << -1;
        return 0;
    }

    cout << rans - lans + 1;

    return 0;
}