#include<fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int hi, lo, mij, p;
int nr_zer(int nr){
unsigned int y = 0, c = 5;
while(nr>=c){
y+=nr/c;
c*=5;
}
return y;
}
int main(){
in >> p;
lo = 1, hi = 5*p;
while(lo <= hi ){
mij = lo+(hi-lo)/2;
if(nr_zer(mij) < p)
lo = mij+1;
else hi = mij-1;
}
if(nr_zer(lo) != p)
out << -1;
else out << lo;
}