#include <bits/stdc++.h>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int n,st,dr,mid,p,nr,rez=-1;

int main()
{
    fin>>n;
    st=1;
    dr=100000000;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        p=1;
        nr=0;
        while(p<=mid)
        {
            p*=5;
            nr+=mid/p;
        }
        if(nr<n)
            st=mid+1;
        else
            if(nr>n)
            dr=mid-1;
        else
        {
            rez=mid;
            dr=mid-1;
        }
    }
    fout<<rez;


    return 0;
}