#include<cstdio>
#include<algorithm>
using namespace std;int n,m,s[26],q[26];
char c[100];
int main(){scanf("%d",&n);for (int i=0;i<26;i++) s[i]=51;while (n--){scanf("%s",c);for (int i=0;i<26;i++) q[i]=0;for (int i=0;c[i];i++) q[c[i]-'a']++;for (int i=0;i<26;i++) s[i]=min(s[i],q[i]);}for (int i=0;i<26;i++)while (s[i]--) putchar('a'+i);
}

#include<cstdio>
#include<algorithm>
#define MN 200001
using namespace std;const int MOD=1e9+7;
int n,m,a[MN],b[MN],A=0,B=0;
int main(){scanf("%d%d",&n,&m);for (int i=1;i<=n;i++) scanf("%d",&a[i]);sort(a+1,a+1+n);for (int i=1;i<=m;i++) scanf("%d",&b[i]);sort(b+1,b+1+m);for (int i=1;i<n;i++) A=(1LL*(a[i+1]-a[i])*i%MOD*(n-i)+A)%MOD;for (int i=1;i<m;i++) B=(1LL*(b[i+1]-b[i])*i%MOD*(m-i)+B)%MOD;printf("%lld\n",1ll*A*B%MOD);
}

#include<cstdio>
#include<algorithm>
#define MN 200001
using namespace std;const int MOD=1e9+7;
int qa[MN],qb[MN],n,x,y,X,Y;
char a[MN],b[MN];
int main(){scanf("%s%s",a+1,b+1);for (int i=1;a[i];i++) qa[i]=qa[i-1]+a[i]-'A'+1;for (int i=1;b[i];i++) qb[i]=qb[i-1]+b[i]-'A'+1;scanf("%d",&n);while(n--){scanf("%d%d%d%d",&x,&y,&X,&Y);puts((qa[y]-qa[x-1])%3==(qb[Y]-qb[X-1])%3?"YES":"NO");}
}

#include<cstdio>
#include<algorithm>
#define MN 1000001
using namespace std;const int MOD=1e9+7;
int n,f[MN],m;
inline void M(int &x){while(x>=MOD)x-=MOD;}
int main(){int i,j;scanf("%d",&n);f[n]=n;m=n-1;for (i=n-1;i;i--) f[i]=1LL*(n-1)*(n-1)%MOD,M(f[i]+=f[i+1]),M(f[i]+=m),M(m+=(i+2>n?1:f[i+2])-1);printf("%d\n",f[1]);
}