#include <cstring>
#include <algorithm>
#include <vector>
#include <cstdio>
using namespace std;

FILE *IN,*OUT;
int pos=0,out=0,sign,N,Ans=0,Total=0,Start,End,c1[26],c2[26];
int first[50005],apear[27],second[26][50005],Val;
char f[131072],Out[131072],str[10],c;

struct _Tree
{
    int Lower,Pos;
}T[132000];
inline void R_Ch(char &ch)
{
 ch=f[pos++];
  if(pos==131072)
            fread(f,131072,1,IN),pos=0;
}
inline void Write_Ch(char ch)
{
    Out[out++]=ch;
    if(out==131072)
        fwrite(Out,131072,1,OUT),out=0;
}
inline void Write_Int(int nr)
{
    int x=0;
    if(nr<0)Write_Ch('-'),nr=-nr;
    do
    {
        str[x++]=nr%10+'0';
        nr/=10;
    }
    while(nr);
    while(x>0)
        Write_Ch(str[--x]);
}
inline int max2(int a,int b)
{
    if (a>b) return a;
    else return b;
}
inline void Read(int &nr)
{
    sign=0;
    nr=0;
    while(f[pos]<'0'||f[pos]>'9')
    {
        if(f[pos]=='-')sign=1;
        pos++;
        if(pos==131072)
            fread(f,131072,1,IN),pos=0;
    }
    while(f[pos]>='0'&&f[pos]<='9')
    {
        nr=10*nr+f[pos++]-'0';
        if(pos==131072)
            fread(f,131072,1,IN),pos=0;
    }
    if(sign)nr=-nr;
}

void Update(int node,int start,int end,int V)
{
 if(start==end)
  T[node].Pos=V;
 else
 {
  int mid=(start+end)>>1;
  if(V<=mid)Update(2*node,start,mid,V);
  else Update(2*node+1,mid+1,end,V);
 }
}
void Query(int node,int start,int end)
{
 if(start==end)
 {
  Ans+=T[node].Pos+T[node].Lower;
  return;
 }
 else
 {
  Ans+=T[node].Lower;
  int mid=(start+end)>>1;
  if(Val<=mid)Query(2*node,start,mid);
  else
  {
   T[2*node].Lower++;
   Query(2*node+1,mid+1,end);
  }
 }
}
int main()
{
    IN=fopen("swap.in","r");
    OUT=fopen("swap.out","w");

    fread(f,1,131072,IN);
 R_Ch(c);
 while(c!='\n')
 {
  c1[c-'a']++;
  first[++N]=c-'a';
  R_Ch(c);
 }
 for(int i=1;i<=N;i++)
 {
  R_Ch(c);
  c2[c-'a']++;
  second[c-'a'][++apear[c-'a']]=i;
  Update(1,1,N,i);
 }
 bool possible=true;
 for(int i=0;i<=25&&possible;i++)
  if(c1[i]!=c2[i])possible=false;
 if(!possible)
 {
  Write_Ch('-');
  Write_Ch('1');
 }
 else
 {
  memset(apear,0,sizeof apear);
  for(int i=1;i<=N;i++)
  {
   Ans=0;
   Val=second[first[i]][++apear[first[i]]];
   Query(1,1,N);
   Total+=Ans-i;
  }
  Write_Int(Total);
 }
 if(out>0)fwrite(Out,1,out,OUT);
    return 0;
}