#include<cstdio>
#include<cstring>
#define mod1 100007
#define mod2 100021
int n,i,j,m,k,l1,l2,mid,o,vec[5],val[100008],minim=1000000;
char s[5][50001],c;
int main ()
{
freopen("subsecvente2.in","r",stdin);
freopen("subsecvente2.out","w",stdout);
scanf("%d%c",&n,&c);
for(i=1;i<=n;i++)
    {
    gets(s[i]);
    vec[i]=strlen(s[i]);
    if(vec[i]<minim)
        minim=vec[i];
    }
l1=1;
l2=minim;
while(l1<=l2)
    {
    mid=(l1+l2)/2;
    int nr1=0,nr2=0,x=1,y=1;
    for(i=0;i<mod1;i++)
        val[i]=0;
    for(i=0;i<mid;i++)
        {
        nr1=((nr1*123)%mod1+s[1][i])%mod1;
        nr2=((nr2*123)%mod2+s[1][i])%mod2;
        if(i!=0)
            {
            x=(x*123)%mod1;
            y=(y*123)%mod2;
            }
        }
    val[nr1]=1;
    for(k=2;k<=n;k++)
        {
        int nrr1=0;
        int nrr2=0;
        int ppp=0;
        for(i=0;i<mid;i++)
            {
            nrr1=(nrr1*123+s[k][i])%mod1;
            nrr2=(nrr2*123+s[k][i])%mod2;
            }
        if(nrr1==nr1&&nrr2==nr2)
            continue;
        for(i=1;i<=vec[k]-mid;i++)
            {
            int x1,y1;
            x1=(x*s[k][i-1])%mod1;
            y1=(y*s[k][i-1])%mod2;
            nrr1=(nrr1-x1+mod1)%mod1;
            nrr2=(nrr2-y1+mod2)%mod2;
            nrr1=(nrr1*123+s[k][i+mid-1])%mod1;
            nrr2=(nrr2*123+s[k][i+mid-1])%mod2;
            if(nrr1==nr1&&nrr2==nr2)
                {
                ppp=1;
                break;
                }
            }
        if(ppp==1)
            continue;
        k=n+3;
        }
    int ppp=0;
    if(k==n+1)
        ppp=1;
    for(j=1;j<=vec[1]-mid&&ppp==0;j++)
        {
        int x1,y1;
        x1=(x*s[1][j-1])%mod1;
        y1=(y*s[1][j-1])%mod2;
        nr1=(nr1-x1+mod1)%mod1;
        nr2=(nr2-y1+mod2)%mod2;
        nr1=(nr1*123+s[1][j+mid-1])%mod1;
        nr2=(nr2*123+s[1][j+mid-1])%mod2;
        if(val[nr1]==0)
            {
            val[nr1]=1;
            for(k=2;k<=n;k++)
                {
                int nrr1=0;
                int nrr2=0;
                int ppp=0;
                for(i=0;i<mid;i++)
                    {
                    nrr1=(nrr1*123+s[k][i])%mod1;
                    nrr2=(nrr2*123+s[k][i])%mod2;
                    }
                if(nrr1==nr1&&nrr2==nr2)
                    continue;
                for(i=1;i<=vec[k]-mid;i++)
                    {
                    int x1,y1;
                    x1=(x*s[k][i-1])%mod1;
                    y1=(y*s[k][i-1])%mod2;
                    nrr1=(nrr1-x1+mod1)%mod1;
                    nrr2=(nrr2-y1+mod2)%mod2;
                    nrr1=(nrr1*123+s[k][i+mid-1])%mod1;
                    nrr2=(nrr2*123+s[k][i+mid-1])%mod2;
                    if(nrr1==nr1&&nrr2==nr2)
                        {
                        ppp=1;
                        break;
                        }
                    }
                if(ppp==1)
                    continue;
                k=n+3;
                }
            if(k==n+1)
                ppp=1;
            }
        }
    if(ppp==0)
        l2=mid-1;
    else
        {
        o=mid;
        l1=mid+1;
        }
    }
printf("%d",o);
return 0;
}