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

long long f(long long n)
{
    long long rez=0;
    while(n>=5)
    {
        n/=5;
        rez+=n;
    }
    return rez;
}

int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    long long p;
    fin>>p;
    if(p==0)
    {
        fout<<0;
        return 0;
    }
    long long st=1,dr=500000000LL,t,sol=-1;
    while(st<=dr)
    {
        t=(st+dr)/2;
        long long val=f(t);
        if(val==p)
        {
            sol=t;
            dr=t-1;
        }
        else if(val<p)
        {
            st=t+1;
        }
        else
        {
            dr=t-1;
        }
    }
    fout<<sol;
    fin.close();
    fout.close();
    return 0;
}