Kattis之旅——Inverse Factorial

 //Asimple
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n, m, num, res, ans, len;string str;
void input() {
    cin >> str;
    len = str.size();
    if( len < 10 ) {
        ll i = 1;
        ll ans = 1;
        while( true ) {
            ans *= i;
            if( ans == atoi(str.c_str()) ) {
                cout << i;
                break;
            }
            i ++;
        }
    } else {
        ll i = 1;
        double ans = 1;
        while( true ) {
            ans += log10(i);
            if( floor(ans)==len ) {
                cout << i;
                break;
            }
            i ++;
        }
    }
}

int main(){
    input();
    return 0;
}