#include <stdio.h>
#include <stdlib.h>
FILE *in,*out;
int nrcifrezero(int a)
{
    int nr = 0,t = -1;
    nr = a/5;
    while(a >= 5)
    {
        t ++;
        a = a/5;
    }
    return nr + t;
}
int cauta(int p)
{
    int a = 0,b = 1000000000,x,y;
    while(a <= b)
    {
        x = (a + b)/ 2;
        y = nrcifrezero(x);
        if(p > y)
            a = x;
        if(p < y)
            b = x;
        if(p == y)
            return x - x%5;
    }
    return -1;
}
int main()
{
    in = fopen("fact.in","r");
    out = fopen("fact.out","w");
    int p,a = 0,b = 1000000000,z;
    fscanf(in,"%d",&p);
    z = cauta(p);
    fprintf(out,"%d",z);
    return 0;
}