#include<bits/stdc++.h>

 using namespace std;

 typedef long long ll;

 typedef unsigned int uint;

 typedef unsigned long long ull;

 typedef pair<int,int> PII;

 typedef pair<ll,ll> Pll;

 typedef vector<int> VI;

 typedef vector<PII> VII;

 typedef pair<ll,int>P;

 #define N  1100010

 #define M  210000

 #define fi first

 #define se second

 #define MP make_pair

 #define pi acos(-1)

 #define mem(a,b) memset(a,b,sizeof(a))

 #define rep(i,a,b) for(int i=(int)a;i<=(int)b;i++)

 #define per(i,a,b) for(int i=(int)a;i>=(int)b;i--)

 #define lowbit(x) x&(-x)

 #define Rand (rand()*(1<<16)+rand())

 #define id(x) ((x)<=B?(x):m-n/(x)+1)

 #define ls p<<1

 #define rs p<<1|1

 const int MOD=,inv2=(MOD+)/;

       double eps=1e-;

       int INF=<<;

       ll inf=5e13;

       int dx[]={-,,,};

       int dy[]={,,-,};

 char a[N],b[N];

 int s[N];

 int n;

 int q,p,id,num[N],F[N],f[N],_f[N],pre[N],len[N],sk[N],df[N],t[N][];

 struct pam

 {

     void add(int x,int n)

     {

             while(s[n-len[p]-]!=s[n]) p=F[p];

         if(!t[p][x])

         {

                 int q=++id,k=F[p];

             len[q]=len[p]+;

             while(s[n-len[k]-]!=s[n]) k=F[k];

             F[q]=t[k][x];

             t[p][x]=q;

             df[q]=len[q]-len[F[q]];

             sk[q]=(df[q]==df[F[q]]?sk[F[q]]:F[q]);

         }

         p=t[p][x];

     }

 }pam;

 int read()

 {

    int v=,f=;

    char c=getchar();

    while(c<||<c) {if(c=='-') f=-; c=getchar();}

    while(<=c&&c<=) v=(v<<)+v+v+c-,c=getchar();

    return v*f;

 }

 int main()

 {

     //freopen("1.in","r",stdin);

     //freopen("1.out","w",stdout);

     scanf("%s",a+);

     int m=strlen(a+);

     scanf("%s",b+);

     int n=;

     rep(i,,m)

     {

         s[++n]=a[i]-'a';

         s[++n]=b[i]-'a';

     }

     s[n+]=s[]=;

     id=F[]=; len[]=-; _f[]=;

     rep(i,,n) f[i]=1e9;

     rep(i,,n)

     {

         pam.add(s[i],i);

         for(int x=p;x;x=sk[x])

         {

             _f[x]=i-len[sk[x]]-df[x];

             if(df[F[x]]==df[x]&&f[_f[x]]>f[_f[F[x]]]) _f[x]=_f[F[x]];

             if(i%==&&f[i]>f[_f[x]]+) f[i]=f[_f[x]]+,pre[i]=_f[x];

             if(i%==&&s[i]==s[i-]&&f[i-]<f[i])

             {

                 f[i]=f[i-];

                 pre[i]=i-;

             }

         }

     }

     //rep(i,1,n) printf("%d ",s[i]);

     //printf("\n");

     if(f[n]==1e9)

     {

         printf("-1\n");

         return ;

     }

     printf("%d\n",f[n]);

     int k=n;

     while(k)

     {

         int t=pre[k];

         if(t<k-) printf("%d %d\n",t/+,k/);

         k=t;

     }

     return ;

 }