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

int main()
{
    FILE *fin, *fout;
    int p, n=0, f, nrz, j=1, i;
    fin=fopen("fact.in", "r");
    fscanf(fin, "%d", &p);
    fclose(fin);
    while(j!=0)
    {
        nrz=0;
        f=1;
        n++;
        for(i=1;i<=n;i++)
            f=f*i;
        while(f%10==0)
                {
                        nrz++;
                        f=f/10;
                }

        if(nrz==p)
            j=0;
    }
    fout=fopen("fact.out", "w");
    fprintf(fout, "%d", n);
    fclose(fout);
    return 0;
}