#include <fstream>
using namespace std;ifstream f("fact.in");ofstream g("fact.out");
int main(){long long x,s=0,j,s1=0,s2=0,s3=0,s4=0,s5=0,s6=0,s7=0,s8=0,s9=0,s10=0,s11=0,s12=0,s13=0;f>>x;
if(x==0) g<<1;else{s=x*5-5*((x-5)/5);for(j=5;j<=500000000;j*=5){s1+=s/j;s2+=(s-5)/j;s3+=(s-10)/j;s4+=(s-15)/j;s5+=(s-20)/j;s6+=(s+5)/j;s7+=(s+10)/j;s8+=(s+15)/j;s9+=(s+20)/j;s10+=(s-25)/j;s11+=(s-30)/j;s12+=(s+25)/j;s13+=(s+30)/j;}
if(x==s1||x==s2||x==s3||x==s4||x==s5||x==s6||x==s7||x==s8||x==s9||x==s10||x==s11||x==s12||x==s13){if(x==s2)g<<s-5;
else
if(x==s3)g<<s-10;
else
if(x==s4)g<<s-15;
else
if(x==s5)g<<s-20;
else
if(x==s6)g<<s+5;
else
if(x==s7)g<<s+10;
else
if(x==s8)g<<s+15;
else
if(x==s9)g<<s+20;
else
if(x==s10)g<<s-25;
else
if(x==s11)g<<s-30;
else
if(x==s12)g<<s+25;
else
if(x==s13)g<<s+30;
else
g<<s;}
else
g<<-1;}}