HIHO1466

#include<bits/stdc++.h>

using namespace std;

#define gc c=getchar()
#define r(x) read(x)
#define ll long long

template<typename T>
inline void read(T&x){
    x=0;T k=1;char gc;
    while(!isdigit(c)){if(c=='-')k=-1;gc;}
    while(isdigit(c)){x=x*10+c-'0';gc;}x*=k;
}

const int N=2e5+7;

struct SAM{
    int Max[N];
    int Min[N];
    int to[N][26];
    int fa[N];
    int sg[N];
    ll cnt[N][27];
    ll sum[N];

    int tot;

    inline int NewNode(int mx,int mi,int *tr,int su){
        ++tot;
        Max[tot]=mx;
        Min[tot]=mi;
        if(tr!=NULL)memcpy(to[tot],tr,26<<2);
        fa[tot]=su;
        sg[tot]=-1;
        return tot;
    }

    inline int extend(int u,int c){
        int t=NewNode(Max[u]+1,0,NULL,0);
        for(;u&&!to[u][c];u=fa[u])to[u][c]=t;
        if(!u){
            Min[t]=1;
            fa[t]=1;
            return t;
        }
        int v=to[u][c];
        if(Max[v]==Max[u]+1){
            Min[t]=Max[v]+1;
            fa[t]=v;
            return t;
        }
        int x=NewNode(Max[u]+1,0,to[v],fa[v]);
        Min[t]=Min[v]=Max[x]+1;
        fa[t]=fa[v]=x;
        Min[x]=Min[fa[x]]+1;
        for(;u&&to[u][c]==v;u=fa[u])to[u][c]=x;
        return t;
    }

    queue<int>Q;

    int calcSG(int u){
        if(~sg[u])return sg[u];
        bool vis[27]={0};
        for(int i=0;i<26;++i){
            if(!to[u][i])continue;
            vis[calcSG(to[u][i])]=1;
            for(int j=0;j<27;++j)cnt[u][j]+=cnt[to[u][i]][j];
        }
        for(int i=0;i<27;++i){
            if(vis[i])continue;
            sg[u]=i;
            break;
        }
        ++cnt[u][sg[u]];
        for(int i=0;i<27;++i)sum[u]+=cnt[u][i];
        return sg[u];
    }

    inline void build(char *s){
        int n=strlen(s);
        int lst=NewNode(0,0,NULL,0);
        for(int i=0;i<n;++i)lst=extend(lst,s[i]-'a');
        calcSG(1);
    }

    inline ll cnt1(int u,int x){
        return cnt[u][x];
    }

    inline ll cnt2(int u,int x){
        return sum[u]-cnt[u][x];
    }

}A,B;

ll k;
char s[N];
char t[N];
char a[N];
char b[N];

inline ll calc(int u,int v){
    ll ans=0;
    for(int i=0;i<27;++i){
        ans+=A.cnt1(u,i)*B.cnt2(v,i);
    }
    return ans;
}

inline int dfsA(int x,int u){
    if(B.cnt2(1,A.sg[u])>=k)return u;
    k-=B.cnt2(1,A.sg[u]);
    for(int i=0;i<26;++i){
        if(!A.to[u][i])continue;
        ll t=calc(A.to[u][i],1);
        if(t<k)k-=t;
        else {
            a[x]=i+'a';
            return dfsA(x+1,A.to[u][i]);
        }
    }
    return 0;
}

inline void dfsB(int x,int u,int v){
    k-=(B.sg[u]!=v);
    if(k==0)return ;
    for(int i=0;i<26;++i){
        if(!B.to[u][i])continue;
        ll t=B.cnt2(B.to[u][i],v);
        if(t<k)k-=t;
        else {
            b[x]=i+'a';
            return dfsB(x+1,B.to[u][i],v);
        }
    }
}

int main(){
    scanf("%lld%s%s",&k,s,t);
    A.build(s);
    B.build(t);
    int t=dfsA(0,1);
    if(!t)return puts("NO"),0;
    dfsB(0,1,A.sg[t]);
    printf("%s\n",a);
    printf("%s\n",b);
    return 0;
}