#include<bits/stdc++.h>
using namespace std;
const int N=200001;
int ind[N];
pair<int,int>tag[N];
vector<pair<int,int>>e[N];
vector<tuple<int,int,int>>res[N];
int ord(int x,int v){
    return (ind[x]>ind[v]||(ind[x]==ind[v]&&x>v));
}
void report(int x,int y,int z,int val){
  //  cout<<x<<" "<<y<<" "<<z<<" "<<val<<endl;
    if(y>z)res[x].push_back({y,z,val});
    else res[x].push_back({z,y,val});
    if(x>z)res[y].push_back({x,z,val});
    else res[y].push_back({z,x,val});
    if(x>y)res[z].push_back({x,y,val});
    else res[z].push_back({y,x,val});
}
void dfs2(int x){
    for(auto [v,val]:e[x]){
        if(!ord(x,v))continue;
        tag[v]={x,val};
    }
    for(auto [v,val]:e[x]){
        if(!ord(x,v))continue;
        for(auto [v2,val2]:e[v]){
            if(!ord(v,v2))continue;
            if(tag[v2].first==x){
                report(x,v,v2,tag[v2].second+val+val2);
            }
        }
    }
}
int solve(int x){
    if(res[x].size()<=1)return -1;
    int max_z,max_y,max_v=-1;
    vector<pair<int,int>>s;
    for(auto [y,z,val]:res[x]){
        if(val>max_v){
            max_v=val;
        }
    }
    int ans=-1;
    for(auto [y,z,val]:res[x]){
        if(val==max_v){
            s.push_back({y,z});
        }
    }
    for(auto [max_y,max_z]:s){
        pair<int,int> fix_y={-1,-1},fix_z={-1,-1};
        int libre=-1;
        for(auto [y,z,val]:res[x]){
            if(max_y==y){
                if(max_z!=z){
                    fix_y=max(fix_y,{val,z});
                }
            }
            else if(max_z==z){
                if(max_y!=y){
                    fix_z=max(fix_z,{val,y});
                }
            }
            else if(max_z==y){
                if(max_y!=z){
                    fix_z=max(fix_z,{val,z});
                }
            }
            else if(max_y==z){
                if(max_z!=y){
                    fix_y=max(fix_y,{val,y});
                }
            }
            else {
        //     cout<<"safe "<<y<<" "<<z<<endl;
                libre=max(libre,val);}
        }
    // cout<<x<<" "<<max_y<<" "<<max_z<<' '<<fix_y.second<<" "<<fix_z.second<<" "<<libre<<endl;
        if(libre==-1&&(fix_y.first==-1||fix_z.first==-1))ans=max(ans,-1);
        else ans=max(ans,max(max_v+libre,fix_y.first+fix_z.first));

        if(ans==max_v*2)return ans;
    }
    return ans;
}
int main(){
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++){
        int x,y,z;
        scanf("%d%d%d",&x,&y,&z);
        e[x].push_back({y,z});
        e[y].push_back({x,z});
    }
    for(int i=1;i<=n;i++){
        dfs2(i);
    }
    int ans=-1;
    for(int i=1;i<=n;i++){
        ans=max(ans,solve(i));
    }
    printf("%d\n",ans);

}