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

int main()
{
    FILE *fin, *fout;
    int n,a,i,t;
    fin=fopen("fact.in","r");
    fout=fopen("fact.out","w");
    fscanf(fin,"%d",&n);
    a=0;
    while(n>0)
    {
      a=a+5;
      i=a;
      t=0;
      while(i%5==0)
      {
        t++;
        i=i/5;
      }
      n=n-t;
    }
    if(a==0)
      a++;
    fprintf(fout,"%d",a);
    fclose(fin);
    fclose(fout);
    return 0;
}