#include <fstream>
#define i64 long long
using namespace std;
char const in [] = "fact.in";
char const out [] = "fact.out";
ifstream f (in);
ofstream g (out);
i64 p;
i64 lastzero (i64 val)
{
    i64 power = 5 , searched = 0;
    while(val / power)
    {
        searched += val / power;
        power *= 5;
    }
    return searched;
}
int main()
{
    f >> p;
    i64 from , to , number ;
    i64 found = -1;
    from = 1 ;
    to = 1LL * (9223372036854775807 ) / 64;
    while(from <= to)
    {
        i64 mid = (from + to) / 2;
        number = lastzero (mid);
        if(number > p)
            to = mid - 1;
        else
            if(number == p)
                found = mid , to = mid - 1;
            else
                from = mid + 1;
    }
    g << found << '\n';
    return 0;
}