#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

ll s, l, k, dp[20], st[20];

void read() {
    cin >> s;
}

ll slowve(ll n) {
    ll ans = 0;
    for (ll k = 1; k <= n; k++) {
        ll p = k;
        while (p) {
            if (p % 10 == 5) ans++;
            p /= 10;
        }
    }
    return ans;
}

void upd(int i, ll &s, ll &l) {
    l += (s % 10) * st[i];
    s /= 10;
}

ll solve(ll n) {
    s = n;
    dp[0] = st[0] = 1;
    for (int i = 1; i < 18; i++) {
        st[i] = st[i - 1] * 10;
        dp[i] = dp[i - 1] * 10 + st[i];
    }
    l = 0;
    k = s % 10 > 4;
    upd(0, s, l);
    for (int i = 1; s; i++) {
        k += dp[i - 1] * (s % 10);
        if (s % 10 == 5) k += l + 1;
        if (s % 10 > 5) k += st[i];
        upd(i, s, l);
    }
//    cout << k;
    return k;
}

signed main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

//    for (ll i = 1; i < 1000; i++) {
//        if (slowve(i) != solve(i)) {
//            cout << i << endl;
//            cout << slowve(i) << ' ' << solve(i);
//            return 0 ;
//        }
//    }
    read();
    cout << solve(s);
}