#include <fstream>
using namespace std; 
int five(int n)
{
int nr=0;
while (n>=5)
{
	n=n/5;
	nr++;
}
return nr;
}
 
int main()
{
    ifstream f ("fact.in"); 
    ofstream g ("fact.out"); 
    
    int div2,p,i;
    f >> p; 
    for (i=0,div2=1<<30;p>0;div2/=2)
        if (five(i+div2)<p)
            i=i+div2;
    if (five(i+1)==p)
        g << i+1; 
    else
        g <<-1;
}