#include<fstream.h>
#include<iostream.h>
int factorial(int n){int i,f=1;
    for(i=1;i<=n;i++){f=f*i;}
    return f;}
int zerouri(int p){int m,n=1,i=0;
while(p%10==0)
{
    i++;
    p=p/10;}
    return i;
}
int main(){int p,j,n=1,m;
    fstream f("fact.in",ios::in);
    while(!f.eof()){f>>p;}
    f.close();
    do{
              j=zerouri(factorial(n));
              m=n;
              n++;}while(j!=p);
    fstream g("fact.out",ios::out);
    g<<m;
    g.close();}