Function main

Codeforces_problems/Bargain/solution.cpp:65–102

int main(int /* argc */, char** /* argv */)
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
#ifdef LOCAL
	assert(freopen("i.txt", "r", stdin));
	assert(freopen("o.txt", "w", stdout));
#endif

	string s;
	cin >> s;

	int n = s.size();
	vector<ll> a(n);
	for (int i = 0; i < n; ++i) {
		a[i] = s[i] - '0';
	}

	const int MOD = (int)1e+9 + 7;

	ll ans = 0;
	ll sum = 0;
	ll p = 1;

	for (ll i = n - 1; i >= 0; --i) {
		ll k = (i * (i + 1) / 2 % MOD * p % MOD + sum) % MOD;
		sum = (sum + p * (n - i) % MOD) % MOD;
		p = p * 10 % MOD;
		ans = (ans + a[i] * k % MOD) % MOD;
	}

	cout << ans << endl;

#ifdef LOCAL
	cerr << "Time execute: " << clock() / (double)CLOCKS_PER_SEC << " sec" << endl;
#endif
	return 0;
}