#include <fstream>

using namespace std;

int main()
{
    ifstream cin("fact.in");
    ofstream cout("fact.out");
    int p, x = 1, d = 1, zero = 1;
    cin>>p;

    if( p == 0 )
        cout<<"1";
    else{
        while( p > 0 ){
        zero *= 10;
        p--;
    }

    while( x % zero != 0 ){
        if( d == 2 || d == 5 || d == 10 )
            x *= d;
        d++;
    }
    cout<<d - 1;
    }


    return 0;
}