#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long p,m,s,n;
int main(){f>>p;
for(n=4*p;s<p;n++) for(m=n,s=0;m!=0;m/=5,s+=m);
if(s!=p) g<<-1; 
else if(p==0) g<<1; 
else g<<n-1;
}