#include <cstdio>

FILE *fin = freopen("fact.in","r",stdin);
FILE *fout = freopen("fact.out","w",stdout);

int p;
int logN;

int verif(int x)
{
    int s = 0;
    for(int i = 5; i<= x; i*=5)
    {
        s+=(x/i);
    }
    return s;
}

int main()
{
    scanf("%d", &p);
    logN = 1 << 31 - 1;
    int k = 0;

    for(; logN ; logN >>=1)
    {
        if(verif(k+logN) < p)
            k+=logN;
    }
    if(k!=0)
        printf("%d",k+1);
    else
        printf("-1");

    return 0;
}