#include<stdio.h>

long int expon(long int k)
{
    long int e=0,a=5;
    
    while(a<=k)
        {
          e+=floor(k/a);
          a*=5;    
        }
    return e;
}
int main()
{
    long int p,k=1;
    FILE *f,*g;
    
    f=fopen("fact.in","rt");
    fscanf(f,"%li",&p);
    fclose(f);
    g=fopen("fact.out","wt");
    while(expon(k)<p)
       {
          k++;    
       }
    if (expon(k)==p) fprintf(g,"%li\n",k);
       else fprintf(g,"-1\n");
   
    fclose(g);

    
    return 0;    
}