#include<stdio.h>
#include<math.h>
int main()
{
long long int P,N,nr=0,nrdenr=0;
int i=0,j,k,aux,x;
FILE*in=fopen("fact.in","r");
FILE*out=fopen("fact.out","w");
fscanf(in,"%lld",&P);


while(nr<P)
{x=1;
i+=5;
nrdenr++;
aux=nrdenr;
while(aux%5==0)
    {aux/=5;x++;}
nr+=x;
}
if(nr==P) fprintf(out,"%d",i);
else fprintf(out,"-1");

fcloseall();
return 0;
}