#include <stdio.h>
FILE *fin , *fout;
int func (int nr)
{
    int suma = 0;
    while(nr>0)
    {
        suma=suma+(nr/5);
        nr/=5;
    }
    return suma;
}

int main()
{
    int n;
    fin = fopen ("fact.in" ,"r");
    fout = fopen ("fact.out" ,"w");
    fscanf(fin ,"%d" ,&n);
    int  i=0;
    int pas = 1<<30;
    while(pas!=0)
    {
        if(func(i+pas)<n)
            i+=pas;
        pas/=2;
    }
    i=i+1;
    fprintf(fout ,"%d" ,i);
    return 0;
}