#include <stdio.h>

int main(){
 unsigned long P,n=1,n0=0,multiplier=1;
 FILE*f=fopen("fact.in","r");fscanf(f,"%ld",&P);
 fclose(f);f=fopen("fact.out","w");
 while(n0<P){
  multiplier++;
  n*=multiplier;
  while(n%10==0){
	n/=10;
	n0++;
  }
  n%=10;
 }
 if(n0>P)multiplier=-1;
 fprintf(f,"%ld",multiplier);
 fclose(f);
 return 0;
}