#include <iostream>
#include <fstream>
using namespace std;
 
ifstream f("fact.in");
ofstream g("fact.out");
 
int p,nr;
long long x,cx;
 
int cautbin(int p)
{
    int st,dr;
 
    if(p==0)return 1;
    st=1; dr=400000000;
    while(st<=dr)
    {
        int m=(st+dr)/2;
        nr=m/5+m/25+m/125+m/625+m/3125+m/15625+m/78125+m/390625+m/1953125+m/9765625+m/48828125+m/244140625;
        if(p==nr) {while (m%5!=0) m--; return m;}
         else if(p<nr) dr=m-1;
            else st=m+1;
    }
 
    return -1;
}
 
 
int main()
{
    f>>p;
    g<<cautbin(p);
    return 0;
}