#include <iostream>
#include<fstream>

using namespace std;
ifstream f ("fact.in");
ofstream g ("fact.out");
int p,st,dr,mij,sol,gasit,cc;
 int zerouri(int x)
{
    int i,s=0;
    for(i=5;x/i>=1;i=i*5)
    {
        s=s+x/i;
    }
    return s;
}

int main()
{f>>p;
st=1;
dr=5*p;
sol=0;
cc=0;
while(st<=dr)
{mij=(dr+st)/2;
gasit=zerouri(mij);
if(gasit==p){sol=mij;dr=mij-1;cc=1;}
else if (gasit<p){st=mij+1;}else dr=mij-1;}
if(cc==0)g<<-1;
else g<<sol;

    return 0;
}