#include <fstream>
using namespace std;
unsigned zerouri(unsigned x)
{int z;
    while(x)
    z=z+x/5;
    x=x/5;
        return z;
}
int main()
{   int st=1,dr=100000000,mijl;
    unsigned N,P;
    ifstream f("fact.in");
    ofstream g("fact.out");
    f>>P;
    while(st<dr){
        mijl=(st+dr)/2;
        if(zerouri(mijl)<P)
            st=mijl;
        else
            dr=mijl;
    }   g<<mijl;

    return 0;
}