#include<cstdio>
using namespace std;

int main()
{
    FILE *f=fopen("fact.in","r"),*g=fopen("fact.out","w");
    int x,facto=1,c=0,i=2,j;
    bool gasit=false;
    fscanf(f,"%i",&x);
    if(x<0)
    {
        fprintf(g,"-1");
    }
    else
    {
        while(c<x)
        {
            facto=facto*i;
            if(i%5==0)
            {
                for(j=i;j>1 && j%5==0;j/=5)
                {
                    c++;
                }
            }
            i++;
        }
        fprintf(g,"%i",i-1);
    }
    fclose(f);
    fclose(g);
    return 0;
}