#include<bits/stdc++.h> using namespace std; int n,k,a[10000][10000],ans; int main(){ cin>>n>>k; for(int i=0;i<=n;i++){ for(int j=1;j<=k;j++){ cin>>a[i][j]; if(i==1){ if(k==0) continue; if(i==2){ if(k!=0) continue; } }else ans++; } } if(ans!=0) cout<<ans; else cout<<"-1"; return 0; }