#include <fstream>

using namespace std;
int n,i,j,s,t[500004];
long long z,x,y,nr[500004];
int main()
{
    ifstream fin("reguli.in");
    ofstream fout("reguli.out");
    fin>>n;
    fin>>y>>x;
    nr[1]=x-y;
    int k=0;
    for (i=3;i<=n;i++)
    {
        fin>>y;
        z=y-x;
        nr[i-1]=z;
        while (k>0 && nr[k+1]!=nr[i-1]) k=t[k];
        if (nr[k+1]==nr[i-1]) k++;
        t[i]=k;
        x=y;
    }
    n--;
    //if (k>=n/2+n%2) fout<<n-k; else fout<<n;
    fout<<n-k;
    return 0;
}