#include<stdio.h>
#include<math.h>
unsigned long p,s=0;

/*int fact5(unsigned long n)
{
              if (n%5==0) return 1+fact5(n/5);
              return 1;
}
*/
int main()
{
    unsigned long i;
    FILE *f=fopen("fact.in","r");
    FILE *g=fopen("fact.out","w");
    fscanf(f,"%lu",&p);
    fclose(f);
    double x=log(5);
    if (p!=0)
       {
       for(i=1;s<p;++i)
            if (i%5==0) s+=1+log(i)/x;
            else ++s;
       if (s==p) fprintf(g,"%lu",5*i-5);
            else fprintf(g,"-1");
       }
    else fprintf(g,"1");
    return 0;
}