#include<stdio.h>
#include<iostream.h>
#include<conio.h>
int main(){
unsigned long p,max,optim,verif=0;
unsigned long i,j,x=0;
clrscr();
FILE *fin=fopen("fact.in","r");
FILE *fout=fopen("fact.out","w");
fscanf(fin,"%lu",&p);
max=p*5;
for(i=5;i<max+1;i+=5){
 j=i;
 while(j%5==0){
  j/=5;
  x++;
 }
}
cout<<x;
optim=x-p;

for(i=max;i>max-5*optim;i-=5){
 if((i/5)%5==0) verif=1;
}
max-=5*optim;
if(verif) fprintf(fout,"%d",-1);
else fprintf(fout,"%lu",max);
fclose(fin);
fclose(fout);
return 0;
}