#include<stdio.h>

long long int a,b,v[12];
int i;

long long int pet(int a, int b)
 
{long long int i=a; if(b==0)return 1;
b--;
while(b--)a*=i;
return a;
}

long long int zero(long long int n)
{long long int x=0;
int i; for(i=1; i<12; i++)x+=n/v[i];

return x;
}








int main(void){

freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);
for(i=1; i<12; i++)v[i]=pet(5,i);


scanf("%lld",a);
b=0;

while(zero(b)<a)

{b+=5;}

if(b>a)printf("%d",-1); else printf("%lld",b);
return 0;
}