#include <bits/stdc++.h>

#define SZ(x) (int) x.size()
#define rep(i,a,b) for (int i = a;i < b;i++)

using ll = long long;
template<typename T> using V = std::vector<T>;
template<typename X,typename Y> bool ckmin(X& x,const Y& y) { return (y < x) ? (x = y,1) : 0;}
template<typename X,typename Y> bool ckmax(X& x,const Y& y) { return (y > x) ? (x = y,1) : 0;}

using std::cin;
using std::cout;
using std::cerr;

constexpr ll MOD = 1e9 + 7;
ll qm(ll x) {
    return x >= MOD ? x - MOD : x;
}
void add(ll& x,ll y) {
    x += y;
    if (x >= MOD) x -= MOD;
}
ll qpow(ll b,ll p) {
    ll ret = 1;
    while (p != 0) {
        if (p & 1) ret = ret * b % MOD;
        p >>= 1, b = b * b % MOD;
    }
    return ret;
}
ll inv(ll x) {
    return qpow(x, MOD - 2);
}

int n;
char s[50][23];

int count(char* s) {
    int cnt = 0;
    while (*s != '\0') {
        if (*s == '?')cnt++;
        s++;
    }
    return cnt;
}

int toInt(char c) {
    return c == '\0' ? 0 : c - 'a' + 1;
}

ll dp[22][51][51][28];
ll rec(int k,int l,int r,int f) {
    ll& ret = dp[k][l][r][f];
    if (ret != -1) return ret;
    if (s[l][k] != '?' && toInt(s[l][k]) != f) return ret = 0;
    if (s[l][k] == '?' && f == 0) return ret = 0;
    if (l == r) {
        ret = qpow(26,count(s[l] + k + 1));
    } else {
        for (int j = l + 1;j <= r;j++) {
            if (s[j][k] == 0) return ret = 0;
        }
        ll ans = 0;
        bool t = 1;
        for (int j = l + 1;j <= r;j++) {
            if (s[j][k] == '?') {
                ll vl = 0,vr = 0;
                for (int jj = f + 1;jj < 27;jj++) {
                    add(vr,rec(k,j,r,jj));
                }
                for (int ff = 0;ff < 27;ff++) {
                    add(vl,rec(k + 1,l,j - 1,ff));
                }
                add(ans,vl * vr % MOD);
            } else if (toInt(s[j][k]) > f) {
                for (int ff = 0;ff < 27;ff++) {
                    add(ans,rec(k + 1,l,j - 1,ff) * rec(k,j,r,toInt(s[j][k])) % MOD);
                }
            }
            if ((s[j][k] != '?' && toInt(s[j][k]) != f) || (f == 0 && s[j][k] == '?')) {
                t = 0;
                break;
            }
        }
        if (t) {
            for (int i = 0;i < 27;i++) {
                add(ans,rec(k + 1,l,r,i));
            }
        }
        ret = ans;
    }
    return ret;
}

void solve() {
    memset(dp,-1,sizeof(dp));
    cin>>n;
    for (int i = 0;i < n;i++) {
        cin>>s[i];
    }
    ll ans = 0;
    for (int i = 1;i < 27;i++) {
        add(ans,rec(0,0,n - 1,i));
    }
    cout<<ans<<'\n';
}

int main() {
    std::ios::sync_with_stdio(false);
    cin.tie(0);
    cin.exceptions(cin.failbit);

#ifdef DEBUG
    freopen("input.txt","r",stdin);
#endif

    solve();

    return 0;
}