#include<stdio.h>
using namespace std;
long int p,i=1,x,s,lol=25;
int main()
{unsigned putere=2;
FILE*f=fopen("fact.in","r");
FILE*g=fopen("fact.out","w");
fscanf(f,"%d",&p);
while(s<p)
{
    if(i==1) i=i+4;
    else i=i+5;
    if(lol/i==1)
    {s=s+putere;putere++;lol=lol*5;
    }
    else s++;
}
if(s==p) fprintf(g,"%d",i);
else fprintf(g,"-1");
fclose(f);
fclose(g);
    return 0;
}