#include <stdio.h>

#include <stdlib.h>

int nrzero(int n){
    int nr=0;
    while(n>=5){
        nr+=n/5;
        n/=5;
    }
    return nr;
}

int main(){
  int n, nr, m;
  FILE *fin, *fout;
  fin=fopen("fact.in", "r");
  fout=fopen("fact.out", "w");
  fscanf(fin, "%d", &m);
  nr=-1;
  n=1;
  while(nr<m){
      nr=nrzero(n);
      n++;
  }
  if(nr==m){
      fprintf(fout, "%d", n-1);
  }
  else{
      fprintf(fout, "-1");
  }
  return 0;

}