#include <iostream>
#include <climits>
#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long zerourifact(long long n)
{
    long long p , s;
    p = 5; s = 0;
    while(p <= n)
    {
        s = s + n/p ;
        p = p * 5;
    }
    return s;
}

long long cb(long long p)
{
    long long st, dr, m, z;
    st = 1; dr = LLONG_MAX;
    while(st <= dr)
    {
        m = (st + dr) /2 ;
        z = zerourifact(m);
        if(z == p)return m;
        else if(z > p)dr = m - 1;
        else st = m + 1;
    }
}

int main()
{
    long long p, z;
    fin >> p;
    z = cb(p);
    while(z % 5 != 0)
        z-- ;
    if(p == 0)fout << 1;
    else
    fout << z;
    return 0;
}