#include<stdio.h>
#include<limits.h>
FILE*fin,*fout;
long  u,p,i,exp,m,ok,nrz,max=LONG_MAX,nr;
int main(){


fin=fopen("fact.in","r");
fout=fopen("fact.out","w");
u=max;
fscanf(fin,"%ld",&nrz);
if(nrz==0){fprintf(fout,"1");}
else{
while(p<=u){
m=(u+p)/2;
nr=0;exp=1;
while(exp<=m){
	exp=exp*5;
	nr=nr+m/exp;


}
if(nr==nrz){fprintf(fout,"%ld",m-m%5);break;}
else{
if(nr<nrz){p=m+1;}
if(nr>nrz){u=m-1;}
}
}




}
if(p>u){fprintf(fout,"-1");}

return 0;}