#include<fstream>
std::ifstream f("fact.in");
std::ofstream g("fact.out");
int zero(int n)
{int ok=0;
for(int i=5;n/i>=1;i*=5)
    ok+=n/i;
return ok;
}
int cautare_binara(int p)
{int left=0,right=5*p+1,middle=-1;
while(left<right)
{
    middle=(left+right)/2;
    if(zero(middle)<p)
          left = middle+1;
        else if(zero(middle)==p)
            return middle - middle%5;
        else
            right = middle-1;
    }
    return -1;
}


int main()
{int p,l,r,mij ;
f>>p;
if(p==0)
  g<<1;
else g<<cautare_binara(p);
return 0;}