func_code_string: #include <bits/stdc++.h>   using namespace std;   template <typename T, typename U>   inline void smin(T &a, const U &b) {     if (a > b) a = b;   }   template <typename T, typename U>   inline void smax(T &a, const U &b) {     if (a < b) a = b;   }   template <class T>   inline void gn(T &first) {     char c, sg = 0;     while (c = getchar(), (c >  9  || c <  0 ) && c !=  - )       ;     for ((c ==  -  ? sg = 1, c = getchar() : 0), first = 0; c >=  0  && c <=  9 ;          c = getchar())       first = (first << 1) + (first << 3) + c -  0 ;     if (sg) first = -first;   }   template <class T1, class T2>   inline void gn(T1 &x1, T2 &x2) {     gn(x1), gn(x2);   }   int power(int a, int b, int m, int ans = 1) {     for (; b; b >>= 1, a = 1LL * a * a % m)       if (b & 1) ans = 1LL * ans * a % m;     return ans;   }   const int mod = 1000000007;   int pt[100100], p2[100100];   int sum[100100], dp[100100], mn[100100], mx[100100];   char s[100100], t[100100];   int calc(char *s, int n) {     int ans = 0, val = 0, pre = 0;     for (int i = 0; i < n; i++) {       int v = (val + 4LL * pt[n - i - 1]) % mod;       if (s[i] ==  7 ) {         ans = (ans + (long long)v * v % mod * (p2[n - i - 1] - 1) +                (long long)v *                    (2LL * sum[n - i - 1] - mn[n - i - 1] - mx[n - i - 1]) +                dp[n - i - 1]) %               mod;         ans = (ans + mod) % mod;         if (pre)           ans = (ans + (long long)(pre + mx[n - i]) * (v + mn[n - i - 1])) % mod;       }       if (s[i] ==  7 )         pre = (val + 4LL * pt[n - i - 1]) % mod;       else if (pre)         pre = (pre + 7LL * pt[n - i - 1]) % mod;       val = (val + (long long)(s[i] -  0 ) * pt[n - i - 1]) % mod;     }     ans = (ans + (long long)val * pre) % mod;     return ans;   }   int main() {     scanf( %s %s , s, t);     int n = strlen(s);     for (int i = pt[0] = p2[0] = 1; i <= n; i++)       pt[i] = 10LL * pt[i - 1] % mod, p2[i] = p2[i - 1] * 2 % mod;     for (int i = 1; i <= n; i++) {       dp[i] =           ((long long)pt[i - 1] * pt[i - 1] % mod * (4 * 4 + 7 * 7) % mod *                (p2[i - 1] - 1) +            11LL * pt[i - 1] % mod * (2LL * sum[i - 1] - mn[i - 1] - mx[i - 1]) +            2LL * dp[i - 1] +            (4LL * pt[i - 1] + mx[i - 1]) % mod *                (7LL * pt[i - 1] % mod + mn[i - 1])) %           mod;       dp[i] = (dp[i] + mod) % mod;       mn[i] = (10LL * mn[i - 1] + 4) % mod;       mx[i] = (10LL * mx[i - 1] + 7) % mod;       sum[i] = (2LL * sum[i - 1] + 11LL * pt[i - 1] % mod * p2[i - 1]) % mod;     }     cout << (calc(t, n) - calc(s, n) + mod) % mod << endl;     return 0;   }   