//  Created by conan1024hao in 2019.
//  Copyright © 2019 conan1024hao. All rights reserved.
//  専用ライブラリです、自由にコピーして構いません。
//  感谢看我的代码！Wechat:conan1024hao QQ:810396815
#pragma GCC optimize ("O3")
#include <iostream>
#include <iomanip>
#include <istream>
#include <ostream>
#include <sstream>
#include <iterator>
#include <vector>
#include <algorithm>
#include <queue>
#include <deque>
#include <list>
#include <stack>
#include <map>
#include <set>
#include <utility>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <ctime>
#include <cctype>
#include <cstdlib>
#define INF 10e16
#define MOD 1000000007
#define rep(i, a, n) for (ll i = a; i < (ll)(n); i++)
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define mmax(x,y)(x>y?x:y)
#define mmin(x,y)(x<y?x:y)
#define chmax(x,y) x=mmax(x,y)
#define chmin(x,y) x=mmin(x,y)
#define all(x) (x).begin(),(x).end()
#define siz(x) (ll)(x).size()
#define PI acos(-1.0)
using namespace std;
using Int=int_fast64_t;
typedef long long int ll;
typedef pair<ll,ll>Pll;
typedef pair<int,int>Pin;
long long GCD(long long a, long long b) { return b ? GCD(b, a%b) : a; }
long long LCM(long long a, long long b)  {return a/GCD(a,b)*b;}
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
ll cmp(pair<ll,string>a,pair<ll,string> b){
        if(a.fi!=b.fi)
        return a.fi<b.fi;
        else
        return a.se<b.se;
}

//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
int main(){//問題をちゃんと見ろ!!!!!!!!!!!!!!!!!      llか??????????
    cin.tie(0);
    ios::sync_with_stdio(false);
    //-------------------------------
    //ex:conteSt contEst coNTEst coNtest ContE
    string s,t;cin>>s>>t;
    vector<int>alp[26];map<char,int>mm;
    for(int i=0;i<s.length();i++){
            alp[s[i]-'a'].pb(i);
    }
    unsigned long long cnt1=0;
    if(alp[t[0]-'a'].empty()){
        cout<<-1<<endl;
        return 0;
    }
    int now=-1;
    map<int,int>m;
    for(int i=0;i<t.length();){
        if(alp[t[i]-'a'].empty()){
            cout<<-1<<endl;
            return 0;
        }
        bool abc=0;
        //cout<<now<<endl;
        for(int j=m[t[i]-'a'];j<alp[t[i]-'a'].size();j++){
            
            //cout<<now<<" "<<alp[t[i]-'a'][j]<<endl;
            if(now<alp[t[i]-'a'][j]){
                now=alp[t[i]-'a'][j];
                m[t[i]-'a']=j;
                abc=1;
                i++;
                break;
            }
        }
        if(abc==0){
            cnt1++;
            m.clear();
            now=-1;
        }
        //if(now==alp[t[i]-'a'][0])
        /*if(alp[t[i]-'a'][]<now){
            cnt1++;
            m.clear();
            if(i<t.length()-1){
            if(alp[t[i+1]-'a'].empty()){
                cout<<-1<<endl;
                return 0;
            }
            now=alp[t[i]-'a'][0];
            //m[t[i]-'a']++;
               // i++;
            }
        }
        else{
            now=alp[t[i]-'a'][m[t[i]-'a']];
            m[t[i]-'a']++;
        }
         */
        //cout<<cnt1<<endl;
    }
    cout<<(unsigned long long)(cnt1*s.length()+now+1)<<endl;
    //-------------------------------
    return 0;
}
//---------------------------------------------------------------------------


Measured memory_bytes: 1228