#include <iostream>
#include <fstream>

using namespace std;

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

int n,p;

int zero(int n){
int nro=0;
while(n>=5){
      nro+=(n/5);
}
return nro;
}



int main()
{
in>>p;
int r=0,pas=1<<28;
while(pas!=0){
if(zero(r+pas)<p){
   r+=pas;
}
pas/=2;
}
r++;
if(zero(r)!=p)r=-1;
out<<r;
return 0;
}