#include <cstdio>

using namespace std;
const int MAX=2000000000;
int fact(int x);

int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int p;

    scanf("%d",&p);
    if(p==0)
    {
        printf("1\n");
        return 0;
    }

    int dr;
    dr=fact(MAX);
    int i, step;
    for (step = 1; step < dr; step <<= 1);
    for (i = 0; step; step >>= 1)
        if (fact(i + step)< dr && fact(i+step)<=p)
           i += step;
    if(i)
    {
        while(i%5)i--;
        printf("%d\n",i);
    }
    else
        printf("-1\n");
    return 0;
}
int fact(int x)
{
    int a=5,rez=0;
    while(x/a)
    {
        rez+=x/a;
        a*=5;
    }
    return rez;
}