#include <stdio.h>

int zero(int n)
{
    int nr=0;
    while(n>0)
    {
        nr+=n/5;
        n/=5;
    }
    return nr;
}
int caut(int p)
{
    int i=0,pas=1<<29;
    while(pas!=0)
    {
        if(zero(i+pas)<p)
            i+=pas;
        pas/=2;
    }
    return i+1;
}

int main()
{
    FILE *in,*out;
    int p,r;
    in=fopen("fact.in","r");
    out=fopen("fact.out","w");
    fscanf(in,"%d",&p);
    r=caut(p);
    if(zero(p)!=r)
        fprintf(out,"%d",r);
    else
        fprintf(out,"-1");
    return 0;
}