#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define fi first
#define se second
#define mkp make_pair
#define pb emplace_back
typedef pair<ll,ll> Pr;
inline ll read(){
	ll x=0, f=1; char ch=getchar();
	while(ch<'0' || ch>'9') { if(ch=='-') f=-1; ch=getchar(); }
	while(ch>='0' && ch<='9') x=x*10+ch-'0', ch=getchar();
	return x*f;
}
const ll dx[4] = {1, 0, 0, -1};
const ll dy[4] = {0, 1, -1, 0};
ll w,d,n,vis[2505],dis[2505],cnt[2505];
ll code(ll i,ll j){ return (i-1)*d+j; }
vector<Pr>E[2505];
ll que[5005],hd,tl;
bool out(ll x,ll y){ return (x<1) || (x>w) || (y<1) || (y>d); }
void solve(){
	w=read(), d=read(), n=read();
	for(ll i=1;i<=n;i++){
		ll x=read(), y=read(), z=read();
		E[0].pb(code(x, y), -z);
		E[code(x,y)].pb(0, z);
	}
	for(ll i=1;i<=w;i++){
		for(ll j=1;j<=d;j++){
			for(ll p=0;p<4;p++){
				ll tx = i+dx[p], ty = j+dy[p];
				if(out(tx, ty)) continue;
				E[code(i,j)].pb(code(tx, ty), 1);
				// cout<<"add "<<i<<","<<j<<" to "<<tx<<","<<ty<<endl;
			}
		}
	}
	memset(dis,0x3f,sizeof(dis));
	que[hd=tl=1]=0; vis[0]=1; dis[0]=0;
	while(hd<=tl){
		ll x=que[hd++];
		vis[x]=0;
		// cout<<"now pop "<<x<<" with "<<dis[x]<<endl;
		for(auto p: E[x]){
			ll y=p.fi, W=p.se;
			if(dis[y]>dis[x]+W){
				dis[y]=dis[x]+W;
				// cout<<"update "<<y<<" as "<<dis[y]<<endl;
				cnt[y]=cnt[x]+1;
				if(cnt[y]>w*d+1){
					// cout<<"node "<<y<<" has "<<cnt[y]<<endl;
					// cout<<"w*d+1="<<w*d+1<<endl;
					puts("No");
					return;
				}
				if(!vis[y]){
					que[++tl]=y;
					vis[y]=1;
				}
			}
		}
	}
	ll ans=0;
	for(ll i=1;i<=w*d;i++) {
		// cout<<"node "<<i<<" has "<<dis[i]<<endl;
		ans-=dis[i];
	}
	printf("%lld\n", ans);
}

int main(){
	#ifdef LOCAL
		assert(freopen("input.txt", "r", stdin));
		assert(freopen("output.txt", "w", stdout));
	#endif
	ll T=1;
	while(T--) solve();		
	return 0;
}