#include<stdio.h>
int nr9(int i)
{   int nr=0;
    while((i%5==0 || i%10==0)&&i!=0)
    {nr++;
    i/=10;
}return nr;
}
int main ()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int n,val=2,i;
    scanf("%d",&n);
    for(i=1;val<=n;i++)
    if(i%5==0 || i%10==0)
    val+=nr9(i);
    printf("%d",--i);
    return 0;
}