#ifdef LOCAL
#include <cstdio>
#include <vector>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdlib>
#else
#include <bits/stdc++.h>
#endif
using namespace std ;

typedef long long ll ;
typedef unsigned long long ull ;
#define rep(i , n ) for ( int i =0; i < n ; i++)
#define rrep(i , n) for ( int i = n-1; i >=0 ; i--)

#define _sort(arg) sort(begin(arg), end(arg))
#define MOD 1000000007
#define pb push_back
#define DEBUG(x) cout << #x << ": " << x << endl;

class UnionFind {
private:
	ull size_; 
	std::vector<ull> par, rank, count;

public:
	UnionFind() : size_(0), par(std::vector<ull>()), rank(std::vector<ull>()), count(std::vector<ull>()) {};
	UnionFind(ull size__) : size_(size__) {
		par.resize(size_); rank.resize(size_); count.resize(size__);
		for (ull i = 0; i < size_; i++) par[i] = i, rank[i] = 0, count[i] = 1;
	}
	ull size() { return size_; }
	// ull root(ull x) { return par[x] == x ? x : par[x] = root(par[x]); }
	
	ull root(ull x)
	{
		while(par[x] != x)
		{
			par[x] = par[par[x]];
			x = par[x];
		}
		return x;
	}
	
	bool same(ull x, ull y) { return root(x) == root(y); }

	void unite(ull x, ull y) {
		x = root(x), y = root(y);
		if (x == y) return;
		if (rank[x] < rank[y]) par[x] = y, count[y]+=count[x], count[x]=0;
		else if (rank[x] == rank[y]) par[y] = x, rank[x]++, count[x]+=count[y], count[y]=0;
		else par[y] = x, count[x] += count[y], count[y] = 0;
	}

	ull size__(ull x)
	{
		return count[root(x)];
	}

	bool operator==(const UnionFind &u) { return par == u.par; }
	bool operator!=(const UnionFind &u) { return par != u.par; }
};
/*
maybe sth wrong 
got wa in one problem
*/
ll modpow(ll a, ll b)
{
	if (b == 0)
	{
		return 1;
	}

	if (b % 2)
	{
		return a * modpow(a, b-1) % MOD;
	}
	else
	{
		ll halfB = b / 2;
		ll half = modpow(a, halfB);
		return half * half % MOD;
	}
}

ll calcComb(ll n, ll m)
{
	if (m > n-m)
	{
		return calcComb(n, n-m);
	}

	ll ansMul = 1;
	ll ansDiv = 1;

	rep(i, m)
	{
		ansMul *= (n-i);
		ansDiv *= (i+1);
		ansMul %= MOD;
		ansDiv %= MOD;
	}

	return ansMul * modpow(ansDiv, MOD - 2) % MOD;
}

__attribute__((constructor))
void initial()
{
	cin.tie(NULL);
	ios::sync_with_stdio(false);
}

const int maxn=2e5+100;
int head[maxn],lazy[maxn],v[maxn];
int size=0;
int n,q;

struct Edge
{
	int to;
	int next;
}e[maxn<<1];

inline void addedge(int u, int v)
{
	e[++size].to = v;
	e[size].next = head[u];
	head[u] = size;
}

void dfs(int u, int p)
{
	v[u] += lazy[u];
	for (int i = head[u]; i; i = e[i].next)
	{
		int to=e[i].to;
		if(to==p)continue;
		v[to]+=v[u];
		dfs(to,u);
	}
}

int main()
{
	string s, t;

	cin >> s >> t;

	int slen = s.size();
	int tlen = t.size();

	int next[slen+1][26];
	rep(i, 26)
	{
		next[slen][i] = -1;
	}

	for (int i = slen; i >= 1; i--)
	{
		memcpy(next[i-1], next[i], sizeof(next[i]));
		next[i-1][s[i-1] - 'a'] = i - 1;
	}

	int tmp = 0;
	int loop = 0;
	bool find = true;

	for (int i = 0; i < tlen; i++)
	{
		int cur = next[tmp][t[i]-'a'];
		if (cur == -1)
		{
			loop++;
			tmp = 0;
			cur = next[tmp][t[i] - 'a'];
			if (cur == -1)
			{
				cout << -1 << endl;
				find = false;
				break;
			}
			tmp = cur+1;
		}
		else
		{
			tmp = cur + 1;
		}
		
	}
	if (find)
	{
		cout << (ll(loop)) * slen + tmp << endl;
	}

	return 0;
}


Measured memory_bytes: 10704