let N = 210;
let M = 20010;
let INF = 0x3f3f3f3f;

let graph = [];
for (let i = 0; i < N; i++) graph[i] = new Int32Array(N).fill(INF);
for (let i = 0; i < N; i++) graph[i][i] = 0;

let floyd = () => {
    for (let k = 1; k <= n; k++) {
        for (let i = 1; i <= n; i++) {
            for (let j = 1; j <= n; j++) {
                graph[i][j] = Math.min(graph[i][j], graph[i][k] + graph[k][j]);
            }
        }
    }
}

let n = 0,
    m = 0,
    k = 0;

let buf = '';
process.stdin.on('readable', function () {
    let chunk = process.stdin.read();
    if (chunk) buf += chunk.toString();
});
let getInputNums = line => line.split(' ').filter(s => s !== '').map(x => parseInt(x));
let getInputStr = line => line.split(' ').filter(s => s !== '');
process.stdin.on('end', function () {
    buf.split('\n').forEach(function (line, lineIdx) {
        if (lineIdx === 0) {
            n = getInputNums(line)[0];
            m = getInputNums(line)[1];
            k = getInputNums(line)[2];
        } else if (lineIdx <= m) {
            let arr = getInputNums(line);
            let a = arr[0];
            let b = arr[1];
            let c = arr[2];
            graph[a][b] = Math.min(graph[a][b], c);
            if (lineIdx === m) {
                floyd();
            }
        } else if (lineIdx <= m + k) {
            let arr = getInputNums(line);
            let a = arr[0];
            let b = arr[1];
            if (graph[a][b] > parseInt(INF / 2)) console.log('impossible');
            else console.log(graph[a][b]);
        }
    });
});