萌新WA求助

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define MOD 1000000007
bool debug = 1;
#define int ll
int quickpow(int a, int b)
{
    int res = 1;
    while (b)
    {
        if (b & 1)
            res = res * a % MOD;
        a = a * a % MOD;
        b >>= 1;
    }
    return res % MOD;
}
signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    string s;
    int k;
    cin >> s >> k;
    int ans = 0;
    int len = s.length();
    for (int i = 0; i < len; i++)
        if (s[i] == '0' || s[i] == '5')
            ans = (ans + (quickpow(2, i) * (quickpow(2, len * k) - 1))  / (quickpow(2, len) - 1)+MOD) % MOD;
    cout << ans;
    return 0;
}