#include<stdlib.h>
#include<stdio.h>

int main(void) {
  FILE *f, *g;
  f = fopen("fact.in", "r");
  g = fopen("fact.out", "w");
  int nr0=0;
  fscanf(f,"%d",&nr0);
  if (nr0==0) {
    fprintf(g,"%d\n",1);
    return 0;
  }
  int min = 0;
  int max = 100000001;
  int mid = -1;
  int cur_nr0 = -1;
  int i = 0;
  while(min <= max) {
    cur_nr0=0;
    mid = (min+max)/2+min;
    for(i=5;i<=mid;i*=5) {
       cur_nr0 += mid/i;
    }
    if (cur_nr0>nr0) max=mid-1; 
    else { 
      if(cur_nr0<nr0) min=mid+1;
      else max=max-1;
    }
  }
  if (cur_nr0==nr0) fprintf(g,"%d\n",mid);
  else fprintf(g,"%d\n",-1);
  return 0;
}