#include <iostream>
#include<fstream>
#include<climits>
using namespace std;
long nr_zero(int n)
{
    long p=0,i;
    for(i=5;i<=n;i=i*5)
        p=p+(long)(n/i);

    return p;
}
int main()
{long long P,st,dr,m,nr;
int N,ok=0;
ifstream fin("fact.in");
ofstream fout("fact.out");
fin>>P;
st=0;
dr=INT_MAX;
while(st<=dr&&ok==0)
{
    m=(st+dr)/2;
    nr=nr_zero(m);
    if(nr==P)
    {
        ok=1;
        N=m;
    }
    else
        if(nr>P)
        dr=m-1;
       else
           st=m+1;
}
if(ok==1)
fout<<N;
else
    fout<<"-1";
    return 0;
}